U.S. patent application number 10/817046 was filed with the patent office on 2004-11-18 for method and system for enabling collaborative authoring of hierarchical documents with associated business logic.
Invention is credited to Coward, Ken, Elza, Dethe, Fergusson, Michael, Flego, Anton.
Application Number | 20040230903 10/817046 |
Document ID | / |
Family ID | 33425239 |
Filed Date | 2004-11-18 |
United States Patent
Application |
20040230903 |
Kind Code |
A1 |
Elza, Dethe ; et
al. |
November 18, 2004 |
Method and system for enabling collaborative authoring of
hierarchical documents with associated business logic
Abstract
A method in a computer system is disclosed for enabling authors
to work on hierarchical documents. The method comprises retrieving
a hierarchical document from a server computing device, modifying
the retrieved hierarchical document, sending an indication of the
modification to the server computing device, and when the
modification cannot be applied on the server computing device,
reverting the modified hierarchical document to a current form of
the hierarchical document on the server computing device. A system
is disclosed for receiving a registration request from a business
logic event handler, registering the business logic event handler,
and performing function relating to indications from the business
logic event handler.
Inventors: |
Elza, Dethe; (Vancouver,
CA) ; Coward, Ken; (Vancouver, CA) ; Flego,
Anton; (Vancouver, CA) ; Fergusson, Michael;
(Vancouver, CA) |
Correspondence
Address: |
PERKINS COIE LLP
PATENT-SEA
P.O. BOX 1247
SEATTLE
WA
98111-1247
US
|
Family ID: |
33425239 |
Appl. No.: |
10/817046 |
Filed: |
April 2, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60471284 |
May 16, 2003 |
|
|
|
60471567 |
May 16, 2003 |
|
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Current U.S.
Class: |
715/234 ;
715/255 |
Current CPC
Class: |
G06F 40/166 20200101;
G06F 40/143 20200101; G06F 40/197 20200101; G06F 40/137
20200101 |
Class at
Publication: |
715/513 |
International
Class: |
G06F 017/21 |
Claims
We claim:
1. A method in a distributed document object model system for
associating business logic, comprising: receiving a registration
request from a business logic event handler for an event of the
distributed document object model; registering the business logic
event handler; and when an event occurs, notifying the business
logic event handler; receiving an indication from the business
logic event handler; and performing a function relating to the
received indication.
2. The method of claim 1 wherein the event handler handles an event
that is generated before a requested mutation is applied to a
document.
3. The method of claim 2 wherein the event handler is registered
for a document type.
4. The method of claim 2 wherein the handler disallows the
requested mutation.
5. The method of claim 2 wherein the handler allows the requested
mutation.
6. The method of claim 2 wherein event handling is performed on a
client computing device.
7. The method of claim 2 wherein event handling is performed on a
server computing device
8. The method of claim 1 wherein the event handler handles an event
that is generated when a requested mutation is applied to a
document.
9. The method of claim 1 wherein the event handler handles an event
that is generated after a requested mutation is applied to a
document.
10. The method of claim 1 wherein the event handler enforces a
business rule.
11. The method of claim 10 wherein a business rule requests a
mutation to a hierarchical document.
12. The method of claim 11 wherein an answer message is sent to a
client that requested a mutation that caused the event handler to
enforce the business rule that requested the mutation.
13. The method of claim 12 wherein a broadcast message is sent to
another connected client.
14. The method of claim 11 wherein the business rule requests the
mutation without a corresponding request from a client.
15. The method of claim 14 wherein a broadcast message is sent to
all connected clients.
16. A distributed document object model system for associating
business logic, comprising: a component that receives a
registration request from a business logic event handler for an
event of the distributed document object model; a component that
registers the business logic event handler; a component that
notifies the business logic event handler when an event occurs; a
component that receives an indication from the business logic event
handler; and a component that performs a function relating to the
received indication.
17. The system of claim 16 wherein the event handler handles an
event that is generated before a requested mutation is applied to a
document.
18. The system of claim 17 wherein the event handler is registered
for a document type.
19. The system of claim 17 wherein the handler disallows the
requested mutation.
20. The system of claim 17 wherein the handler allows the requested
mutation.
21. The system of claim 17 wherein event handling is performed on a
client computing device.
22. The system of claim 17 wherein event handling is performed on a
server computing device
23. The system of claim 16 wherein the event handler handles an
event that is generated when a requested mutation is applied to a
document.
24. The system of claim 16 wherein the event handler handles an
event that is generated after a requested mutation is applied to a
document.
25. The system of claim 16 wherein the event handler enforces a
business rule.
26. The system of claim 25 wherein a business rule requests a
mutation to a hierarchical document.
27. The system of claim 26 wherein an answer message is sent to a
client that requested a mutation that caused the event handler to
enforce the business rule that requested the mutation.
28. The system of claim 27 wherein a broadcast message is sent to
another connected client.
29. The system of claim 26 wherein the business rule requests the
mutation without a corresponding request from a client.
30. The system of claim 29 wherein a broadcast message is sent to
all connected clients.
Description
CROSS-REFERENCES TO RELATED APPLICATION(S)
[0001] This patent application claims the benefit of U.S.
Provisional Patent Application Nos. 60/471,284 and 60/471,567,
which were both filed on May 16, 2003 and entitled "DISTRIBUTED
DOCUMENT OBJECT MODEL" and are both incorporated herein by
reference in their entirety.
TECHNICAL FIELD
[0002] The described technology relates generally to collaborative
authoring, and more particularly to methods and systems for
enabling collaborative authoring of hierarchical documents in a
distributed computing system.
BACKGROUND
[0003] Documents can be described by using an extensible markup
language ("XML"). Such documents may be termed XML documents and
described in a hierarchical manner. A hierarchical document may
need to be manipulated to add, remove, or modify portions of the
document. Such manipulations may be performed in a variety of ways
including directly by modifying XML "tags" that describe the
document or programmatically by using a Document Object Model
("DOM").
[0004] The DOM is an application programming interface ("API")
specification established by the World Wide Web Consortium ("W3C").
The W3C defines the DOM as "a platform- and language-neutral
interface that will allow programs and scripts to dynamically
access and update the content, structure and style of documents."
(<www.w3c.org/DOM>.) The DOM presents a programming interface
for well-formed XML documents, including valid HTML, and defines
how to manipulate a Document Object, such as an XML document. Using
the DOM, a software program can, e.g., create a document, navigate
its structure, and add, retrieve, modify, or delete its
contents.
[0005] The DOM presents a tree view of the XML document. An XML
tree comprises "elements" in which the "documentElement" is the
top-level element of the tree. The documentElement may have one or
more "childNodes" that represent the branches of the tree. A
software program may use the DOM's Node Interface to read and write
elements in the XML tree. As an example, the following VBScript
code uses the DOM to traverse nodes of an XML document and write
the nodeValue of each element that is a child of the
documentElement:
1 for each x in xmlDoc.documentElement.childNodes
document.write(x.nodeName) document.write(": ")
document.write(x.nodeValue) next
[0006] A tree representation of a hierarchical document appears in
FIG. 1. The following is an XML representation of the unshaded
elements of the hierarchical document illustrated in FIG. 1:
2 <library text="Seattle"> <floor text = "1"> <shelf
text = "A"> <book text = "Romeo and Juliet"/> <book
text = "Macbeth"/> </shelf> </floor>
</library>
[0007] FIG. 2 illustrates the relationship between DOM modules as
defined by the W3C and the interfaces available for working with
documents.
[0008] The DOM defines objects, methods, properties, and events. As
an example, the DOM defines a "Document" object that has a
"getElementById" method. An example property of an object is
"nodeValue" and an example event is "DOMNodeInserted." One skilled
in the art will understand that an object model such as the DOM
would have multiple objects, methods, properties, and events, and
would further understand what they are used for and how they
interrelate. The remainder of this specification assumes a baseline
understanding of the current XML and DOM art beyond what is
described above. This baseline is defined by the W3C DOM
specifications, which include Document Object Model (DOM) Level 2
Core Specification Version 1.0 (W3C Recommendation Nov. 13, 2000),
Document Object Model (DOM) Level 2 Events Specification Version
1.0 (W3C Recommendation Nov. 13, 2000), Document Object Model (DOM)
Level 2 HTML Specification Version 1.0 (W3C Recommendation Jan. 9,
2003), Document Object Model (DOM) Level 2 Style Specification
Version 1.0 (W3C Recommendation Nov. 13, 2000), Document Object
Model (DOM) Level 2 Views Specification Version 1.0 (W3C
Recommendation, Nov. 13, 2000), and Document Object Model (DOM)
Level 2 Traversal and Range Specification Version 1.0 (W3C
Recommendation Nov. 13, 2000). These specifications are available
at <http://www.w3.org/DO- M> (last visited Oct. 1, 2003) and
are all hereby incorporated herein by reference.
[0009] Authors sometimes work together when collaborating on a
single document, such as presentation slide decks, books, or
research papers. When the authors are working simultaneously on a
document, they may want to see mutations (e.g., additions,
deletions, updates, or other changes) made by other authors as soon
as those mutations are made. The W3C DOM specification does not,
however, provide a mechanism for multiple people or software
programs to work collaboratively on a single XML document. The W3C
DOM specification also does not provide a mechanism for people
working on different computers to work on the same XML document
simultaneously.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a block diagram illustrating a hierarchical
document.
[0011] FIG. 2 is a block diagram illustrating the relationship
between DOM modules as defined by the W3C.
[0012] FIG. 3 is a block diagram illustrating an embodiment of the
components of the system.
[0013] FIG. 4 is a block diagram illustrating the components of
FIG. 3 in more detail and illustrating some communications
occurring in the system.
[0014] FIG. 5 is a flow diagram illustrating an embodiment of the
Load Document routine.
[0015] FIG. 6 is a flow diagram illustrating an embodiment of the
Connect Document routine.
[0016] FIG. 7A is a flow diagram illustrating an embodiment of the
Mutate Tree routine.
[0017] FIG. 7B is a block diagram illustrating an embodiment of how
the DDOM system may handle multiple mutation requests to add a node
to a document.
[0018] FIG. 7C is a block diagram illustrating an embodiment of how
the DDOM system may handle multiple mutation requests to change the
value of an attribute of a node of a document.
[0019] FIG. 7D is a block diagram illustrating an embodiment of how
the DDOM system may handle multiple mutation requests to change the
value of a data element in a document.
[0020] FIG. 8 is a flow diagram illustrating an embodiment of the
Broadcast Mutation routine.
[0021] FIG. 9 is a flow diagram illustrating an embodiment of the
Mutation Applicable? routine.
[0022] FIG. 10A is a flow diagram illustrating an embodiment of the
Mutation Request routine.
[0023] FIG. 10B is a flow diagram illustrating an embodiment of the
Apply Mutation routine.
[0024] FIG. 11 is a flow diagram illustrating an embodiment of the
Receive Message routine.
[0025] FIG. 12 is a flow diagram illustrating an embodiment of the
Roll Forward routine.
[0026] FIG. 13 is a flow diagram illustrating an embodiment of the
Roll Back routine.
[0027] FIG. 14 is a block diagram illustrating an embodiment of the
communications stack of the DDOM system.
[0028] FIG. 15 is a block diagram illustrating an embodiment of the
content of a DDOM frame.
[0029] FIG. 16 is a block diagram illustrating an embodiment of a
call execution pattern of the DDOM system in synchronous
communications mode.
[0030] FIG. 17 is a block diagram illustrating an embodiment of a
call execution pattern of the DDOM system in asynchronous
communications mode.
[0031] FIG. 18 is a block diagram of an embodiment of the DDOM
system's notification execution pattern.
DETAILED DESCRIPTION
[0032] Methods and systems for enabling collaborative authoring of
hierarchical documents are provided. In an embodiment, a
distributed document object model ("DDOM") system enables multiple
authors using different computing systems to author portions or all
of a hierarchical document. These authors may work on the same or
different portions of the document simultaneously or at different
times. In one scenario of use, an author opens a document on a
client computer for editing. The client computer ("client")
requests the document from a server computer ("server"). The
server, upon determining that the requested document has not
already been opened, opens the document by, e.g., loading it from
storage or requesting a system to create the document. The server
then sends a copy or subset of the document to the client. The
client is then said to be "subscribed" to the document. The user of
the client is able to view the document's contents and make
mutations to the document. These mutations are then propagated to
the server for application to the server's document. When
additional users open the same document, the server sends a copy of
the document, as it presently exists on the server, to the client
of each new user. Any further mutations made by any user are
propagated from the user's client to the server, and then broadcast
from the server to the other clients. In this way, one master
version of the document is maintained by the server, the copy of
each client is updated as mutations are made, and the users can see
the mutations broadcast by the server. This results in a
synchronized view of the document for all users.
[0033] This synchronization between clients and servers is enabled
by various components of the DDOM system acting together. The
components of the DDOM system may include the DOM, a DOM tree
structure, client and server extensions to the DOM, extensions to
the DOM tree structure, and a DDOM communications scheme.
MULTI-USER SYSTEM
[0034] The DDOM is a multi-user system that stores documents and
enables multiple authors to manipulate those documents using
computers that may be connected by a network. The system provides
components for sending and receiving notifications and other
communications relating to mutations made to documents. In one
embodiment, the DDOM system is a middleware layer that routes
mutation events between a central canonical hierarchical document
(i.e., a master version of the document) and multiple remote copies
of the document. The DDOM system may handle collaborative issues
including, e.g., locking, node identity management, mutation
collision avoidance and resolution, and event notification. As a
result, the DDOM system enables multiple authors to have a
"real-time" view of the current state of the document.
[0035] The DDOM system may function in a client/server environment.
In such an environment, a master version of a hierarchical document
is available from a server. Multiple clients may request the server
to load the document and to manipulate portions of the document.
Each client may have a local copy of the document. Multiple clients
may simultaneously be working on the document. In the client/server
environment, there may be a client-side DDOM component and a
server-side DDOM component. The server-side DDOM component is
responsible for opening documents when requested by clients and
providing a copy to the clients, manipulating a master version of
the document as requested by clients, distributing mutations to
clients so they can update their local copies, providing a locking
mechanism for controlling access to portions of documents,
providing a versioning mechanism so various versions of the
document can be accessed as needed, and so on. The client-side DDOM
component provides an interface between application programs that
access the documents and the server-side DDOM component. The
interface allows an application program to open documents, request
mutations, receive mutations from the server-side DDOM component,
and so on.
[0036] Alternatively, the DDOM system may function in a
peer-to-peer environment. In such an environment, one peer
computing device may have a master version of the document and may
be considered a "server" of the master version. The other peer
computing devices may connect with the peer having the master
version so that mutations made to a local copy of the document by a
user can be sent to the peer having the master version.
[0037] Software components of the DDOM system may be used in
conjunction with other software components or products. As an
example, a word processing software product may use the client-side
DDOM components to access and manipulate documents. The DDOM
components may be accessed by software components or products
written in various languages including, e.g., Python, Java,
JavaScript, VBScript, C, C++, C#, and Visual Basic.
[0038] Operations initiated by a client in the DDOM system may be
characterized based on at least three modes: a tree update mode, a
local handler mode, and an invocation mode.
[0039] The tree update mode specifies whether mutations are to be
applied to the master version or a local copy of the document
first. The tree update mode can be either "local before server" or
"server before local." In the "local before server" tree update
mode, a mutation is applied on the local copy of the client
requesting the mutation before the mutation request is sent to the
server. This mode may be used, e.g., when the client must be very
responsive or a connection speed between the client and its server
is slow. In the "server before local" tree update mode, a mutation
is applied on the server to the master version of a document before
the mutation is applied to the local copy of the client that
requested the mutation. This mode may be used, e.g., when the
client is connected to a highly responsive server over a high-speed
network, or a mutation collision is probable and the client cannot
tolerate operations on document states that might not occur on the
master version of the document.
[0040] The local handler mode specifies when handlers of the client
that requests a mutation are to be executed. A handler may perform
specialized processing relating to a mutation. For example, a
handler may cause further mutations based on a user-initiated
mutation. The local handler mode can be asynchronous or
synchronous. When in an asynchronous local handler mode, local
handlers are invoked after local mutations are made regardless of
whether the mutations were successfully applied on the server.
Asynchronous local handler mode may be used, e.g., when the client
must be very responsive or a connection speed between the client
and its server is slow. When in a synchronous local handler mode,
local handlers are not invoked until the mutations are successfully
applied on the server. Synchronous local handler mode may be used,
e.g., when the client is connected to a highly responsive server
over a high-speed network, or a mutation collision is probable and
the client cannot tolerate operations on document states that might
not occur on the master version of the document.
[0041] The invocation mode specifies whether requests to the server
are handled asynchronously or synchronously. When a function (e.g.,
to make a mutation) is invoked at a client asynchronously, the
function may return immediately. Asynchronous invocation mode may
be used, e.g., when the client must be very responsive or a
connection speed between the client and its server is slow. When
the function is invoked synchronously, it does not return until the
server completes its processing. Synchronous invocation mode may be
used, e.g., when the client is connected to a highly responsive
server over a high-speed network or a mutation collision is
probable and the client wants to know when the method call
returns.
[0042] A local change made by a client before the change is applied
on a server may need to be rolled back if the client receives a
conflicting message from the server. As an example, if a client
receives a broadcast message from a server indicating a mutation
that conflicts with a mutation made by a local handler operating
asynchronously, the client may need to reinterpret the server's
message in view of the state of the local copy of the document,
which may result in the need to roll back its local mutation.
Similarly, a client operating in local before server tree update
mode may be instructed by the server to readjust its local tree to
conform with the master version's current state if the server is
unable to apply a requested mutation. This might happen, e.g., when
another client makes a conflicting mutation. The client uses a
local history of mutations to roll back its local mutations.
[0043] Various combinations of the above modes may be used. It is
not necessary, for example, that a "local before server" tree
update mode must be used with a synchronous local handler mode or
invocation mode. It may be possible to use a synchronous local
handler mode with an asynchronous invocation mode, for example.
NODE IDENTITIES
[0044] The DDOM system has a node identity system that facilitates
operation in a multi-user distributed environment. How nodes are
identified (i.e., node schema) may affect factors including, e.g.,
message sizes, node lifecycle management, caching methods and
performance, document loading schema and performance, event
propagation, privileges and security, ability to recover from
crashes, and document persistence. Node identification systems can
be placed in at least two groups: structure-dependent and
structure-independent. Structure-independent node schemas separate
identification of a node from the structure in which the node
appears. Structure-dependent node schemas combine identification
with structure. While the remainder of this specification describes
the use of structure-independent node schemas, structure-dependent
node schemas are equally contemplated.
[0045] A node identity may be either system-unique or
document-unique. When a node identity is system-unique, the node
identity will always refer to a specific node across all documents
of a DDOM system. On the other hand, when a node identity is
document-unique, the node identity may be reused in documents to
refer, e.g., to a node in a first hierarchical document and another
node in a second hierarchical document.
[0046] A unique node identity ("node UID") may be either
session-independent or session-dependent. A session-independent
node identity is static and does not change from one session to
another. A session-dependent node identity may represent one node
in a session and a different node in a second session.
[0047] The combination of the uniqueness and session attributes of
node identities yields four possibilities for node identities:
system-unique/session-independent, system-unique/session-dependent,
document-unique/session-independent, and
document-unique/session-dependen- t. Each of these four
combinations is considered below.
[0048] A system-unique/session-independent node identity is a
unique identification for a node. Such a node UID enables document
persistence, system recovery, and assignment of identifiers by a
client to a node created by it. To support this type of node UID,
the system stores an indication of an association between nodes and
identities. As an example, the client or server may generate
globally unique identities. These identities may then be persisted
with the document using node attributes of a DDOM namespace.
[0049] A system-unique/session-dependent node UID may not be used
because a DDOM system typically does not load and use all documents
in a session.
[0050] A DDOM system may use document-unique/session-independent
node UIDs. The DDOM system may either store indications of an
association between nodes and identities outside the document
containing the nodes or may store the indications inside. Which of
the two approaches is selected may depend on a number of factors
including, e.g., whether the DDOM system is being used by
third-party software and whether compatibility is desired with
legacy documents whose structure or schema cannot be modified. When
the indications are stored in a secondary document separate from a
primary document containing the nodes, the DDOM system may either
need to prevent the schema of the primary document from being
modified or may need to create the secondary document anew with the
assistance of the process that modified the schema. When
indications are stored within the primary document, the DDOM system
may treat nodes that do not have a DDOM-assigned node UID as new
nodes.
[0051] A DDOM system may use document-unique/session-dependent node
UIDs. When such node UIDs are used, a server of the system may need
to create and use a log of activities relating to a document so
that when the document is loaded during a new session, the node
UIDs appear to be static across sessions. Doing so makes this
approach similar to the document-unique/session-independent
approach described above with the addition of document-related
logs.
[0052] The discussion below relates to an embodiment using
document-unique/session-independent node UIDs with the primary
document containing the node UIDs. However, additional embodiments
are contemplated using other schemes for implementing node UIDs
described above.
PRIVILEGES
[0053] The DDOM system supports a concept of privileges. Privileges
relate to what operations and functionality a user may access on
the system and, more particularly, what operations a user may
perform on a node. Descendants of a node inherit an ancestor's
privileges in an embodiment. Alternatively, the DDOM system may
disable inheritance of privileges by children of a node.
[0054] A user may have any combination of Read, Insert, Delete, and
Update privileges on a node or may have no privileges whatsoever. A
user having a privilege may be referred to as an owner or holder of
the privilege. When a user has the Read privilege for a node, the
user can, e.g., access the node's element name, invoke methods on
the node relating to the read operation, and perform other
navigation-related activities on the node.
[0055] When a user has the Insert privilege for a node, the user
can, e.g., make some changes to the subtree beginning at the node.
As an example, the user may be able to append children and set
attributes. When a user has Insert privileges on a node, the user
can also read the node.
[0056] When a user only has the Insert privilege (and not the Read
privilege), some read operations may nonetheless be allowed. As
examples, the user may be allowed to get the name or attributes of
an element. However, operations that require knowledge of the
subtree may not be allowed. As examples, the user may not be
allowed to call an InsertBefore method or access any attributes
relating to the node's children. If a user appends a child to a
node for which the user has only the Insert privilege, subsequent
operations on the child would fail.
[0057] When a user has the Delete privilege for a node, the user
can, e.g., remove the node, its children, or its attributes. The
user may be able to invoke some methods on the parent of the node
such as RemoveChild.
[0058] When a user has the Update privilege for a node, the user
can, e.g., modify attributes and values relating to the node.
[0059] The DDOM system supports a concept of privilege groups.
Users may be members of privilege groups. A privilege group extends
similar privileges to all of its members. A user of the DDOM system
may define privileges for privilege groups relating to document
types. A document type is similar to a W3C XML schema file or XML
Document Type Definition. As an example, the system may have a set
of privilege groups for expense reports and another set of
privilege groups for purchase orders. A user may be able to approve
expense reports but not purchase orders.
[0060] The DDOM system may filter messages sent to a user such that
only nodes the user is privileged to read may appear in the
message. An advantage to using privilege groups is that messages
sent from the server to clients may only need to be filtered by the
number of privilege groups that have connected users instead of the
total number of connected users.
[0061] The API relating to privileges include calls to, e.g., set
privileges, get privileges, and determine whether a certain
privilege (e.g., Read, Insert, Delete, or Update) is available.
These APIs may be applied per user or group on a node or subtree.
The server may be able to determine which privilege group a
requesting client belongs to. The server may validate the request
based on the client's privilege.
NODE LOCKING
[0062] The DDOM system provides a node locking mechanism. This
mechanism provides a client or group of clients with exclusive
access to portions of a document by locking the portions. The node
locking mechanism of the DDOM system enables locking of individual
nodes, groups of nodes, or sub-trees in a document. When a node is
locked, users who do not "own" the lock may not be able to, e.g.,
set attributes on the node, make mutations on the node such as
change its parent, attach or detach children of the node, reorder
children of the node, or unlock the node. A node may have various
characteristics relating to locking. As examples, a node may not
permit locking, may have a maximum lock lease time, or may be
grouped for application of common characteristics. The state of the
locks may be persisted for a given document between sessions or
locks may be removed at the end of a session.
[0063] The DDOM system supports a concept of lock leases. A lock
lease is the maximum duration of time during which a node can be
locked. A node may inherit its maximum lock lease time from its
parent or a maximum lock lease time may be declared for the node
using an API method or property. Further, if a node does not
inherit a maximum lock lease time from a parent and a maximum lock
lease time has not been declared for the node, the node may inherit
its maximum lock lease time from the document. The maximum lock
lease time may have one of several values indicating, e.g., that
the node may not be locked, the node may be locked for an infinite
period of time, or the node may be locked for a specified duration
of time. The lease may be "renewable" in that an application
program may attempt to renew a lock lease before the lease
expires.
[0064] The DDOM system supports a concept of deep locks. Deep locks
are locks placed on a parent node and its descendant nodes. Deep
locks may be complete or partial, and partial locks can be
contiguous or non-contiguous. When a complete deep lock is
requested, all descendants of a specified parent node must be
locked or the lock request will fail. When a non-contiguous lock is
requested, the system attempts to lock all lockable nodes in a
sub-tree that are unlocked, including the descendants of nodes that
are not lockable. A contiguous partial deep lock does not attempt
to lock descendents of nodes in the subtree that cannot be locked.
As an example, if node C and node D are children of node B which is
a child of node A, and a non-contiguous deep lock is requested on
node A when node B is unlockable, the system may lock nodes A, C,
and D. In contrast, if a contiguous lock is requested in a similar
circumstance, the system would only lock node A because node B
could not be locked. A request for a complete lock would fail in
this case because all nodes in the subtree beginning at node A are
not lockable.
[0065] The DDOM system supports a concept of lock bags. A lock bag
contains a collection of locked nodes. Lock bags enable grouping of
nodes for application of various characteristics that, when
applied, apply to all nodes in the lock bag. As an example, a
maximum duration for which a lock may be maintained may be applied
to a lock bag. When that is done, all nodes contained in the lock
bag may be locked for a maximum of the specified time. When a deep
lock is requested, the type of deep lock (e.g., complete,
contiguous, or non-contiguous) may be configured by characteristics
of the lock bag. A lock bag can be given an identification, such as
a name, and may be subsequently manipulated using its
identification.
[0066] A lock bag may allow shared ownership and in such a
situation, owners may be primary or secondary. Secondary owners may
only be able to take lock-related actions on nodes in a lock bag
such as setting a lock lease time. A primary owner, on the other
hand, would have all rights a secondary owner has, but also has
rights to identify other owners of the lock bag and be able to set
characteristics on locks. When shared ownership is not available,
only the owner of the lock may be able to take lock-related
actions.
[0067] Rules govern how nodes and their descendants are locked when
the nodes are moved into and out of a lock bag. These rules may
consider whether a node is unlocked when it is moved out of a lock
bag. They may further consider whether a node will be locked when
it is moved into a lock bag and whether this lock will be deep. As
an example, a lock bag might specify that nodes moved out of the
lock bag become deep unlocked. As another example, if a deep lock
has been placed that includes the moved node and its descendants,
then the moving of the node may cause both the node and its
descendants to become members of the new lock bag. These rules may
also consider whether both lock bags are owned by the same user. An
administrator of the DDOM system or a software application program
may programmatically be able to modify some of these rules.
Alternatively, these rules may not be modifiable.
[0068] "Coercion" rules specify situations that may trigger errors
when a node is moved. As an example, if a node has a shorter lock
lease time than the lock lease time of the bag it is being moved
into, an error or exception may be triggered by a coercion rule. As
a further example, if a node's maximum lease time is shorter than
the lease time of the bag into which the node is being moved, an
error may be triggered. Alternatively, if the maximum lease time of
the bag would be reduced if the node is moved into the bag, an
error may be triggered. In various embodiments, coercion rules may
be specified by, e.g., an administrator, an application program, or
the DDOM system in a manner similar to the rules described above
for lock bags.
[0069] The DDOM system defines an API for its locking mechanism.
This API is comprised of several methods and properties. These
methods and properties may relate to individual nodes, lock bags,
or other grouping of nodes.
[0070] The DDOM system's locking mechanism may also support the
concept of privileges. If a user only has Read or Write privileges
on a node (i.e., and no other privilege), that user may not be able
to lock the node and the locking mechanism may deny a request to
place a lock. This is done to prevent a user with limited access
from blocking updates to the node by other users. When a client
requests a deep lock, the subtrees beginning at nodes for which the
requesting user only has Insert privileges may not be locked
because the user does not have Read privileges on such
subtrees.
DDOM MUTATIONS
[0071] Mutation operations that alter the structure of shared
documents may require interaction between the clients and server of
the DDOM system. Clients send mutation requests to the server and
process mutation notifications received from the server. As an
example, clients may send the server a message indicating that a
node has been added to a tree of the document or removed from the
tree. The server processes mutation requests from clients, notifies
clients of changes made to the master version of the document, and
supplies responses to client-initiated mutation requests. When a
node is removed from the document by a client, the server may place
the node in a pool of removed nodes to track node removals. Removed
nodes may be cleared from the pool as part of a garbage collection
activity.
[0072] The client may perform operations on DDOM fragments. DDOM
fragments are subtrees that are under the client's control and are
not yet attached to the master document. When the client performs
mutation operations on a DDOM fragment, the client does not need to
interact with the server. Clients may begin interacting with the
server in relation to mutation operations on a DDOM fragment after
the fragment is attached to the document. The DDOM client may use
DDOM fragments to assemble a number of nodes and mutation
operations before forwarding the fragments and operations to the
server. In one embodiment, DDOM fragments do not generate DDOM
events. In an alternate embodiment, DDOM fragments generate DDOM
events. There may be methods in the DDOM API relating to DDOM
fragments.
[0073] A DDOM server may perform mutations on the server document
in an asynchronous manner without client-initiated requests. These
asynchronous mutations may be the result of external events
monitored by a business logic component of the server. As an
example, the business logic component may monitor a financial
database and cause mutations to occur to a document based on
changes in the database. These mutations may then be broadcast to
connected clients.
VERSIONING
[0074] The DDOM system supports versioning of documents. Any
arbitrary version of a document can be recreated in the DDOM system
using a snapshot and mutation messages. A snapshot of a document
may be periodically stored in a version storage associated with the
server. This snapshot completely describes a document at a certain
time. The DDOM system also may store messages relating to mutations
made to the document. These messages may be stored in a message
storage. The system can then "roll forward" or "roll back" a
document to its state at any time by applying or removing mutations
to a snapshot.
[0075] To locate a "document version," the DDOM system may first
locate a snapshot that is "near" the desired version. Proximity may
be determined based on version numbers or time. Attributes other
than version number or time may also be used to specify, locate, or
recreate a version of a document. As examples, a version may be
specified using a mutation number or combination of attributes such
as a time and a mutation number. As an example, the fourth mutation
made on Oct. 1, 2003 may be requested.
ILLUSTRATED EMBODIMENT
[0076] Turning now to the figures, FIG. 3 is a block diagram
illustrating components of an embodiment of the DDOM system. The
system 300 includes one or more clients 302, a server 304, and a
network 306. One skilled in the art will recognize that even though
a single network and server are illustrated, there may be multiple
networks, sub-networks, or servers in the system. As an example, a
client may be behind a firewall in an intranet system, yet be
communicating over an Internet to the server, which in turn may be
on a separate intranet. The client and server may be any of a
variety of forms of computing systems. As examples, a client may be
a personal computer, personal digital assistant, advanced cellular
telephone, or a pocket computing device. As further examples, the
server may be a personal computer, mainframe computer, or
minicomputer. One skilled in the art will recognize that computing
devices of different forms and on separate communication networks
are capable of communicating with one another to send or retrieve
various forms of data. Each DDOM client component 308 of a client
has a DDOM document that is a copy of the server's master version
of the document. This master version is handled by the DDOM server
component 310 of the server. The master version of the document and
the clients' copies are represented as tree structures. The DDOM
client and DDOM server components expose the DOM API and DDOM's
extensions to the API. In this embodiment, the DDOM client
components, DDOM server component, and network comprise the DDOM
system.
[0077] FIG. 4 is a block diagram illustrating further details and
components of the system illustrated in FIG. 3. In the embodiment
of the DDOM system 400 illustrated, a client 401 comprises a client
software program 402, a DDOM client component 404, and a DDOM
Protocol Adapter and Message Layer 406. The client software program
may be, e.g., a word processing program, a graphics editor, or any
arbitrary editor of XML or other hierarchical documents. The DDOM
client component performs various client-side processing functions
of the DDOM system including managing the client's copy of the DDOM
document. The client software program may use the DDOM system by
subscribing to and using the API provided by the DDOM client
component.
[0078] Subscribing to the DDOM system includes instantiating a DDOM
document on a client and synchronizing with the document's master
version, which may be located in a server. Synchronizing includes
changing the client's copy of the document as per instructions
received from a server that are designed to make the client's copy
similar to the master version of the document.
[0079] Communications between a client and a server in the DDOM
system may be in the form of messages, which may be in XML form.
These messages include, e.g., mutation requests from clients to a
server, answers from the server to the requesting client, and
broadcasts from the server to clients. DDOM messages are exchanged
between a DDOM client component and a DDOM server component.
[0080] The client software program may make all DOM-related
requests through the DDOM client. The DDOM client may send Mutation
Requests 418 to the server 407 through the DDOM protocol adapter
and message layer. Such communications between client and server
components may occur over a network 413. A DDOM client issues
Mutation Requests to a DDOM server 410 for a document. The Mutation
Requests may contain, among other things, a document identifier, a
client identifier, and one or more mutations. Client and document
identifiers may not be provided in all Mutation Requests, but this
information may be available to client and server message
processors from prior requests. The DDOM Protocol Adapter and
Message Layer may package requests made by the DDOM client into
frames or packets that are acceptable by the communications
protocol being used to communicate with the server. As an example,
if the request has 1024 Kb of data but the protocol accepts a
maximum payload of 128 Kb, the DDOM Protocol Adapter and Message
Layer may break the request down into several packets or frames of
128 Kb each. Similarly, the DDOM Protocol Adapter and Message Layer
of the client may accept information from the server and convert it
into a form acceptable by the DDOM client. This may include
assembling several packets or frames into a larger DDOM
message.
[0081] The server includes a server software program 408, a DDOM
server, a DDOM Protocol Adapter and Message Layer 412, a Version
Storage 414, and a Message Store 416. The server software program
may or may not be related to the client software program. The
server software program is a server-side application program that
may provide enhanced functionality relating to a hierarchical
document that is being authored by a user at a client. As an
example, the server software program may enforce business logic
that causes further mutations to the document based on the
requested mutations. The DDOM server component performs various
server-side processing functions of the DDOM system including
managing the server's master version of the DDOM document.
[0082] A DDOM client may send a Mutation Request to the DDOM server
based on a mutation made by a user of the client software program.
When the Mutation Request from the client arrives at the server,
the DDOM Protocol Adapter and Message Layer of the server may
transform the arriving packets or frames into a form acceptable by
the DDOM server.
[0083] The DDOM server may have event handlers that were registered
by a server component such as the server software program. These
event handlers may be called when the applied mutations cause
events to be fired. As an example, if an employee attempts to
submit an expense report exceeding $500, the server software
program, previously having registered an event handler, may mutate
the expense report's authorization section to, e.g., require a
director's approval in addition to a manager's approval.
[0084] The server may further include a version storage that may be
comprised of snapshots of the hierarchical document created at
various times and a list of modifications made to the document. The
server may also include a message storage that may be used to
re-broadcast messages. The message storage may also be used in lieu
of the list of modifications stored in the version storage. The
list of modifications may be used with the snapshots to recreate a
document as it existed at any time (described below).
[0085] The server, after making mutations to its master version of
the document, may respond with an answer 420 to the requesting
client containing information relating to whether the requested
mutations were successfully applied or reasons for one or more
failures and information relating to the state of the document as
it currently exists on the server. The answer may also contain
information relating to further mutations made by the event
handlers that may have been caused as a result of the requests made
by the client. The server may also send a broadcast 422 to clients
indicating mutations that have been made to the hierarchical
document. The broadcast message may be "pushed" by the server, or
may be "pulled" by the client. Communications from the DDOM server
to the DDOM client are converted into packets or frames
transportable by the communications protocol underlying the DDOM
Protocol Adapter and Message Layer. The underlying communications
protocols may be, e.g., HTTP, TCP/IP, or UDP.
[0086] Both clients and servers may maintain a list of messages
they send. As an example, clients may maintain a list of mutation
requests and servers may maintain lists of answers and broadcasts.
These lists may be kept to resend messages previously sent. A
client may resend a mutation request if it fails to receive an
acknowledgement from the server. A server may resend an answer if
the client so requests or if it determines that the client did not
receive the answer. The server may also maintain a list of
broadcast messages for the purpose of resending broadcasts
requested by a client. Messages sent from clients or servers may
contain a sequence number to easily identify which messages are to
be resent.
[0087] A client or a peer may periodically send "heartbeat"
messages. These heartbeat messages may have the same structure as
mutation requests but may contain no mutation requests and may
contain an indication of the last message received at the client
from the server or sent to the server. A heartbeat message may be
used to keep a connection open between a client and server. A
server may respond to heartbeat messages by sending all mutations
made to the master document that the client may not be aware
of.
[0088] The DDOM Protocol Adapter and Message Layers on the client
and server may also attempt to detect and correct for the loss of
messages. Messages may be lost as a result of an unreliable
protocol layer underlying and being used by the system. The DDOM
Protocol Adapter and Message Layers may attempt to guarantee
delivery of messages by using sequence numbers. As an example, if a
DDOM protocol adapter and message layer receives a message sequence
number 10 after a message sequence number 8, the layer may
recognize that message sequence number 9 has been lost and may
request redelivery of that message. As another example, a
client-side DDOM protocol adapter and message layer, after having
sent a request to a server-side DDOM protocol adapter and message
layer, may wait for a certain period of time for an answer. If that
time elapses without having received an answer, the client-side
layer may assume that the message has been lost and may attempt to
resend the message. As another example, the heartbeat message may
contain information relating to messages that have been sent or
received. The recipient of the heartbeat message may then be able
to determine whether some messages have been lost and attempt to
resend those messages. Either a client or a server that detects
that a message has not been received or has detected that a series
of messages have not been received, may attempt to recover these
lost messages by sending a request to the other to request the
missing message(s). In the unlikely event that a requested message
cannot be resent, a response message may be sent indicating that
the requested messages are not available.
[0089] FIG. 5 is a flow diagram illustrating an embodiment of the
Load Document routine. The routine 500 is executed by the DDOM
client when a client software program first requests to open of a
document. The routine starts at block 502 and is provided with an
indication of the document that is to be loaded. The routine may
optionally authenticate the user at block 504. One skilled in the
art will recognize that various forms of authentication may be
used. The forms of authentication used may depend on the operating
environment of the client, the server, and the client and server
software programs. Authenticating a user may include, e.g.,
ensuring that the user is authorized to use the client, execute the
software programs, or open the document. In an embodiment, if the
user has no privileges relating to any node of the document, the
user may receive an empty document. Alternatively, the user may
receive an error. The routine may call the connect document
subroutine at block 505, which is further described below. At block
506, the routine retrieves the contents of the document and ends at
block 508.
[0090] The DDOM system supports a concept of lazy loading. Using
this technique, a client may load only a subset view of the
document (i.e., a pruned tree), and only load additional portions
of the data as needed. When this is done, the client needs to
recognize when a more complete view must be retrieved from the
server to, e.g., apply a mutation to a portion of the tree the
client does not presently have. In responding to mutation requests
(described further below), the server may include context
information sufficient to inform the client of a node's ancestry
(i.e., its position relative to the document's root node). This
context information may include sufficient information for the
client to decide if it has the node and its ancestors. When a
client recognizes that it has insufficient information relating to
a node, it evaluates this ancestry information to determine whether
it needs to request additional nodes of the document from the
server. The server may use an aspect of the versioning feature
(discussed above) to construct a representation of the tree to
respond to a client's request.
[0091] In an embodiment, clients ignore broadcast messages from the
server relating to nodes that do not appear in the portion of the
document the client has loaded. In an embodiment, clients load
portions of the document relating to received messages.
[0092] FIG. 6 is a flow diagram illustrating an embodiment of the
connect document routine. The connect document routine 600 may
execute on a server computing device when the system runs in a
client/server environment. The routine may also run on any peer
computing device when the system runs in a peer-to-peer
environment. The routine begins at block 602 where it receives an
identifier of a document as a parameter. At block 604, the routine
determines whether the specified document has already been loaded.
If the document has not already been loaded, the routine loads the
document at block 606. Loading the document may involve reading a
portion (or all of) the document from storage. The routine ends at
block 608.
[0093] When a server serializes (i.e., stores) a document, node
UIDs are serialized as node attributes on each of the nodes. In an
embodiment, the attribute is named `ddom:nodeID.` When
document-unique node UIDs are used, the root element of the
document may have an attribute named `ddom:lastIDused` that holds
the node UID that was used previously within the document. Each
text node in the document is identified by an attribute in its
parent non-text node named `ddom:textNodesIDs` which contains a
delimited list of node UIDs for each child text node in the order
in which they appear. The DDOM system may also add additional
attributes.
[0094] When a server de-serializes (i.e., loads) a document that a
DDOM system has not previously serialized or de-serialized, it may
contain no DDOM attributes. This situation triggers a handler which
adds a `ddom:nodeID` attribute to each node of the document and
numbers each such attribute consecutively. A document that has been
previously de-serialized has this attribute at all nodes with
possibly the exception of nodes added by an external system. Such
nodes are assumed to be new and are assigned consecutive node UIDs
starting with the value 1+`ddom:lastIDused.` Text nodes are
identified by attributes set in their parent node, as described
above.
[0095] In an embodiment, node IDs are not sequentially numbered,
but may comprise other unique indications including, e.g.,
alphanumeric characters. In such a case, the expression
"1+`ddom:lastIDused`" refers to a subsequent unique node ID.
[0096] The DDOM system may also need to respond to various problems
relating to DDOM documents. If a `ddom:lastIDused` attribute is not
found on the root element but it is found on some other element,
the DDOM system assumes that another application outside the DDOM
system has restructured the document in such a manner that the
original root node has been moved deeper into the document. If a
`ddom:lastIDused` attribute is not found at all within the
document, but other types of DDOM attributes are found, the DDOM
system triggers an error. In such a case, the default behavior is
to reject the input. However, if a handler is registered for the
error, the handler may perform some other action to resolve the
error.
[0097] An example of a persisted document appears below:
3 <?xml version="1.0" encoding="UTF-8"?> <project
xmlns:ddom="http://ddom.com/schema" ddom:nextNodeID="19"
ddom:nodeID="2" creationDate=" " ddomProjectDocID=" " new="true"
projectOngoing="true" ddom:textNodesIDs="3;18"
ddom:textNodesLockBagIDs="-1;-1"> <ddom:lockBags/>
<document ddom:nodeID="4" creationDate=" " currentDraftNo="0"
documentState="NotReady" name=" " nextDraftNo="1"
ddom:textNodesIDs="5;17" ddom:textNodesLockBagIDs="-1;-1">
<participants ddom:nodeID="6" ddom:textNodesIDs="7;16"
ddom:textNodesLockBagIDs=- "-1;-1"> <current ddom:nodeID="8"
ddom:textNodesIDs="9;11;13;15" ddom:textNodesLockBagIDs="-1;-1;
-1;-1"> <authors ddom:nodeID="10"/> <administrators
ddom:nodeID="12"/> <reviewers ddom:nodeID="14"/>
</current> </participants> </document>
</project>
[0098] FIG. 7A illustrates a flow diagram for an embodiment of the
Mutate Tree routine. This routine makes use of a node locking
mechanism of the DDOM system.
[0099] The DDOM system defines an API for its node locking
mechanism comprising several methods and properties. The following
methods and properties relate to nodes: an isLocked( ) method that
returns a boolean indication of whether the node is locked; a
getLockholder( ) method that returns a string identifying the user
who holds a lock on the node; a lock method whose parameters
include the identification of a lock bag and a boolean indication
of whether a deep lock is desired that returns an indication of
whether the lock was successful or not, and pertinent other
information such as the maximum lease time, remainder time of the
lock, or failure codes or messages; an unlock method that accepts a
boolean indication of whether a deep unlock is desired that returns
a number of nodes unlocked; a get lock bag identification method
that returns an identification of the lock bag containing the node;
a hijack method which enables a user or process with a certain
credential to "steal" a node or lock bag that has been locked by
another user or process; and a canUnlock( ) method that returns an
indication of whether the user calling the method has the necessary
privileges to unlock the node.
[0100] The API relating to lock bags has several methods and
properties including, e.g.: a get ID method returns an
identification of the bag; a get name method returns an indication
of the name of the bag; a get holder method returns an indication
of the user holding the lock bag; a get remaining lease time method
returns an indication of the amount of time remaining in the lease
for the bag; a set bag characteristics method sets characteristics
for the lock bag specified in its parameters; a get bag
characteristics method returns a list of the characteristics that
are presently set on the bag; a delete bag method deletes the lock
bag; a lock node method accepts as parameters a node and a boolean
indicating whether the lock should be deep and returns a results
set relating to whether the lock was successfully placed; an unlock
node method returns the number of nodes unlocked and receives as
parameters a parent node and a boolean indicating whether the
unlock should be deep; an unlock all method attempts to unlock all
nodes and returns the number of nodes actually unlocked; a get
nodes method returns a list of nodes; a get size method returns the
number of nodes in the lock bag; and a renew lease method attempts
to renew a lease on the lock bag and returns the amount of time for
which the lease has been renewed.
[0101] The locking mechanism of the DDOM system may make use of a
"bag characteristics" object. This object exposes an API to
manipulate characteristics of locks, including, e.g.: maximum
duration for which a lock can be maintained; time until a lock
expires; when to notify clients of impending lock expiry; how an
inserted node is treated; how a removed node is treated; whether
the bag allows for a reduction in its maximum lease time when a
node with a shorter lease time is added to the bag; a concept of
"deep lock" modes wherein deep locks may include locks on a parent
and its children nodes; whether a deep lock fails when it cannot
lock all nodes in the subtree; and how lock bags are treated in
regards to persistence when a user disconnects from the server
(e.g., destroyed, persisted, or persisted when the lock bag is not
empty). When a node is added to or removed from a lock bag, the
lock lease time characteristic of the bag may be recalculated. As
an example, when a node is added to a bag and that node has a lock
lease time of 5 seconds and the lock lease time of the bag is 10
seconds, the lock lease time of the bag may be reduced to 5
seconds. Nodes have a lease time that may be specified for the node
or inherited from a parent node. For example, when a node is moved
to a new parent, the node may inherit a lock lease time from its
new parent. While a lock lease time of a bag may be affected by the
addition of a node, the bag's lock lease time may not be
recalculated when the node is moved to a new parent.
[0102] There may also be additional method calls that are
counterparts of similar calls in the DOM. As an example, the DOM
has a "remove attribute" method call. Similarly, the DDOM system
also offers a "remove attribute" method call. An exhaustive list of
DOM method calls that are also implemented in the DDOM system is
unnecessary as one skilled in the art would recognize that all DOM
method calls can be implemented in a DDOM system.
[0103] The DDOM system may have method calls relating to nodes. As
examples, there may be an InsertBefore method for inserting a node
before a specified node. This method may take parameters such as
information relating to the new node and a synchronization mode. A
response from the server to the InsertBefore method may contain an
indication of whether the insertion was successful, a position of
the newly inserted node, and additional information relating to
other mutations that may have been applied on the server. The
operation may fail if the specified node was removed or has a
parent that is different than the parent indicated in the client's
copy of the document. Similarly, there may be method calls to
replace a child node, remove a child node, and append a child
node.
[0104] There may also be method calls relating to the entire
document. As examples, there may be method calls for creating a
lock bag, getting an identification of the owner of a bag, getting
a bag's characteristics, getting a list of bags that are owned by
the user, getting a list of bags, getting an indicating of whether
a bag can be hijacked, and deleting a bag.
[0105] One skilled in the art would recognize that many of these
methods require additional parameters that would be necessary to
implement the method in various embodiments. One skilled in the art
would also recognize that these methods may be invoked
individually, together, or in various combinations.
[0106] Method calls invoked on a client may be transformed into
DDOM messages for sending to a server and vice versa. As an
example, when a client calls the get lock holder method, the DDOM
client may send a message to the DDOM server to retrieve
information relating to who the current holder of a lock is. When
information requested is available locally at the client, the DDOM
client may return the local information instead of requesting the
information from the server.
[0107] When a server responds with its answer, it may return a
positive or negative response. In the case of a client requesting
information relating to the identification a lock holder, a
positive response may include an identification of the holder of
the lock. In this case, a negative response may be an indication of
a server exception based on the fact that the client is not
privileged to request such information. Similarly, when the client
requests a lock on a list of nodes, the client may send the server
an XML message identifying the nodes. In response, the server may
answer with a list of the nodes that have been locked, or may
respond with server exceptions. As another example, a client
requesting to set characteristics relating to a lock bag may submit
a list of the characteristics it desires to change in XML form. In
response, the server may answer with a list of the characteristics
actually changed. In this case, the server may respond with a
different set of characteristics than those requested by the
client. As an example, a client may request a lease duration of 30
seconds but the server may respond with a lease duration of 20
seconds.
[0108] The server may use the routine 700 to receive and process
mutation requests from clients sequentially. Alternatively, the
server may process requests from a given client sequentially, but
may not guarantee that all requests from all clients are processed
sequentially. In other words, whereas a server may process mutation
requests from client A sequentially and may also process mutation
requests from client B sequentially, it may process a
later-arriving request from client B before an earlier request from
client A, thereby interleaving the requests.
[0109] The routine 700 may run on a server computing device or a
peer computing device that holds the master version of a document.
The routine begins at step 701, where it receives as parameters a
mutate message indicating mutations that are requested by the
caller of the routine and an indication of the client that is
making the request.
[0110] At block 702, the routine parses the mutate message received
at step 701 to determine what mutations are requested. The routine
may parse the message based on a message format that is associated
with the client application that is using the DDOM system. The
routine may transform the message into a canonical form that
defines the information content that will be used to effect the
mutation. At block 704, the routine determines whether the
requested mutation is applicable. The determination of whether the
mutation is applicable is a subroutine that is further described
below in relation to FIG. 9. The subroutine may return an
indication of TRUE or FALSE corresponding to whether or not the
mutation is applicable. If the mutation is applicable, the routine
continues at block 706. Otherwise, the routine continues at block
716.
[0111] At block 706, the routine determines whether the requested
mutation will violate lock rules. As an example, a locked node may
not be capable of being moved, and an attempt to move the node
would violate a lock rule. If a lock rule will be violated by the
mutation, the routine continues at block 716. Otherwise, the
routine continues at block 708.
[0112] At block 708, the routine applies the requested mutation. If
the requested mutation is to create a new node, the routine may
create the new node in the tree, set the appropriate attributes,
generate an ID for the newly created node, and assign the new node
this ID. If the client is working in client before server tree
update mode, the client may assign a temporary or local ID to newly
created nodes at the client. Because the server assigns a new ID to
newly created nodes, the ID assigned by the client may not be the
same as the ID assigned by the server. However, it may be possible
for the user to continue to mutate the tree at the client before
the client receives a response from the server. Further mutations
made by the user until such time may reference the client's local
or temporary ID in subsequent messages to the server. As a result,
the server may maintain a mapping of IDs created by clients to IDs
assigned by the server. When the node creation at the server is
successful, the server's answer to the client may include an
indication that temporary IDs have been assigned new server IDs.
Once the client has processed the response from the server, the
client may refer to the new server-assigned ID when sending
subsequent mutation requests to the server. Other examples of
mutations requested by a client or a peer to a DDOM server
component may include:
[0113] Insert node: inserts a node into the document structure;
[0114] Modify attribute: modifies an attribute; if the named
attribute does not exist, it may be added;
[0115] Modify character data contents: modifies the contents of a
CharData or CDATA type node;
[0116] Remove attribute: removes a specified attribute from the
specified node;
[0117] Remove node: removes the specified node from the document
structure;
[0118] Replace child: replaces a node in the document structure
with a specified node; this node can either already exist in the
document structure or be outside the document structure; or
[0119] Set attribute: modifies the value of a specified attribute;
if the attribute does not exist, it is added.
[0120] The routine may lock the relevant portion of the tree using
methods of the API described above so that the mutations can be
made without interference from conflicting requests from other
clients.
[0121] One skilled in the art will recognize that as additional
methods are added to the DOM, additional related methods or
messages may also be added to the DDOM to support similar
functionality.
[0122] Messages containing commands may be sent either from the
client to the server upon a user making mutations at the client, or
may be sent from the server to a client for the client to
incorporate mutations made by a user of another client. There may
be differences in the parameters or message data based on whether
the messages or commands emanate from a client or a server. As an
example, when a client creates a new node, the client may assign
and identify a temporary or local ID as described above. However,
when the server sends a message to a client to create a new node,
the server may already have assigned an ID to the newly created
node and so further use of a temporary ID may not be required.
[0123] At block 710, the routine may add an entry relating to the
mutation(s) just made into a list of mutations made to the tree.
The entry may be added to a version storage, message store, or
both. (Version and message storage components were described above
in relation to FIG. 4.) At block 712, the routine constructs an
answer message and a broadcast message. The answer and broadcast
messages may comprise information relating to the mutation and the
current state of the document. The routine then may continue at
both blocks 713 and 714 (e.g., as two threads). At block 713, the
routine may call the Broadcast Mutation subroutine (which is
further described below in relation to FIG. 8). At block 714, the
routine sends the answer constructed at block 712 to the caller of
the routine. After both blocks 713 and 714, the routine continues
at block 718.
[0124] At block 716, the routine returns a failure to the caller of
the routine, and includes relevant other information. Other
information may include information relating to mutations that have
been made to the tree by this and other requests. As an example,
sufficient information may be provided to synchronize the document
of a caller of the routine with the master version. The routine
ends at block 718 and returns execution to its caller. In an
embodiment, the routine does not return until performing both
blocks 713 and 714.
[0125] FIG. 7B is a block diagram illustrating how addition of
nodes to a document are communicated between a server and clients
in an embodiment of the DDOM system. In the illustrated example,
initially two clients and a server all have a node, "A," in a
hierarchical document. Subsequently, a user of the first clients
add a node, "B," as a child of node "A." At the same time, a user
of the second client adds a node "C" as a child of node "A." When a
client adds a node, the client requests the addition of the node to
the server, as described above. Suppose the request from the first
client arrived at the server before the request from the second
client. In such a case, the server determines that node "B" has
been added as a child of node "A." The server communicates the
successful addition of node "B" to the first client and broadcasts
the addition to all other clients--here the second client. When the
second client receives the broadcast from the server, it adds node
"B" as a second child of node "A." However, because the server
processed the request from the first client before the request from
the second client, node "C" is the second child of node "A" in the
master version of the document at the server, in contrast to the
second client's local copy. The server then returns an indication
of successful addition of node "C" to the second client. However,
the server also indicates a position of node "C" in that message
such that the second client is able to rearrange the children of
node "A" in its local copy of the document in such a manner that
the document continues to be a consistent reflection of what is on
the server. The server then broadcasts the addition of node "C" to
all the other clients--here, the first client. The broadcasts and
responses sent by the server may contain positional information
relating to the tree mutations requested by the clients.
[0126] FIG. 7C is a block diagram illustrating how mutations to a
document relating to attributes of a node are handled by a server
in an embodiment of the DDOM system. In the presented example, two
clients and a server have a hierarchical document with a node "A"
that has a "name" attribute, which is set to "Alice." Suppose a
user of the first client changes the attribute to "Bob." This
client subsequently sends a mutation request to the server. Suppose
further that a user of the second client also changes this
attribute to "Tom" at the same time and this request is received by
the server after the mutation request from the first client. The
server may send an indication of success to the first client, and
broadcast the mutation to all the other clients. The server may
next handle the mutation request from the second client and change
the attribute value to "Tom." The server would then send an
indication of success to the second client and broadcast the
attribute change to all the other clients. Because the attribute
change from the second client was handled after the attribute
change from the first client, both clients and the server now have
"Tom" as the value of the "name" attribute. To ensure that all
clients have a consistent document, responses to mutation requests
may contain not only an indication of success, but also an
indication of mutations made to the master version of the document
on the server.
[0127] FIG. 7D is a block diagram illustrating how the DDOM system
may handle requests for replacing data relating to nodes in a
hierarchial document in an embodiment of the DDOM system. In the
example illustrated, two clients and a server have a hierarchial
document that contains a node "A" which has a related data value
and which is set to "ABCD." Suppose a user of the first client
changes the data value to "EFGH" and at the same time a user of the
second client changes the value of the same data element to "IJKL."
Further suppose that the mutation request from the first client
arrives at the server before the mutation request from the second
client. The server may send an indication of a successful mutation
to the first client and broadcast the mutation to the second
client. After this occurs, the server and both clients reflect a
data value of "EFGH." Subsequently, the server may process the
mutation request from the second client. After making the change on
its master version of the document, the server may send an
indication of success to the second client and broadcast the
mutation to the first client. The broadcast and the indication of
success may contain an indication of the new value for the data
element. After both clients incorporate the mutation sent by the
server, both clients and the server again reflect consistent values
for the data element.
[0128] FIG. 8 illustrates a flow diagram for an embodiment of the
Broadcast Mutation routine. The routine 800 begins at block 802
where it receives an indication of a broadcast message and a
requester as parameters. At block 804, the routine selects the
first group from the list of privileged group relating to the
document. At block 806, the routine filters the broadcast message
according to the privileges of the selected privileged group. As an
example, if the selected group does not have sufficient privileges
to read a node appearing in the broadcast message, that node would
be removed from the broadcast message. Prior to creating a filtered
broadcast message, the routine may first determine whether any
client in the selected privileged group is currently online. At
block 808, the routine selects the first client in the selected
privileged group that is presently online. At block 810, the
routine sends the filtered broadcast message to the selected
client. The routine may not send the filtered broadcast message to
the selected client if the selected client is the requester.
[0129] At block 812, the routine selects the next client in the
selected privileged group. If at block 814 there are no more online
clients, the routine continues at block 816. Otherwise, the routine
continues at block 810. At block 816, the routine selects the next
privileged group. If at block 818 there are no more privileged
groups, the routine continues at block 820. Otherwise, the routine
continues at block 806. At block 820, the routine returns execution
to its caller.
[0130] FIG. 9 illustrates a flow diagram for an embodiment of the
Mutation Applicable? routine. This routine determines whether a
requested mutation is applicable. The routine 900 begins at step
902, where it receives a message indicating the requested mutation
and the client requesting the mutation as parameters. The mutation
message may contain several mutation requests. If that is the case,
the routine may check the applicability of each mutation request
individually. At block 904, the routine determines whether the
requested mutation is a "create" request. If that is the case, the
routine continues at block 906. Otherwise, the routine continues at
block 908. At block 906, the routine determines whether the
requester has sufficient privileges to create a node of the
requested type. The routine may check server-side business logic
associated with the document to determine whether the node should
be created. As an example, an engineer may not be authorized to
create a new account to which expenses are charged. If the node can
be created, the routine continues at block 916. Otherwise, the
routine continues at block 918.
[0131] The routine determines at block 908 whether a node ID
specified in the requested mutation is in the the hierarchical
document. If the node UID is not in the document, the routine
continues at block 918. The server may receive and recognize both
clients' local node UIDs and server node UIDs. If the node UID is
in the tree, the routine continues at block 910. As described above
in relation to FIG. 7, a client may create a node locally and
assign a temporary node UID to the node. The server may or may not
have seen the temporary node UID from the client. The server may
assign a node UID to the new node when the server adds the node to
its master version of the document. The server may also maintain a
mapping from temporary node UIDs to server-assigned node UIDs. It
may do this because the client may send additional mutations
relating to the new node before receiving an indication from the
server that the server has assigned a node UID to the node. Once
the server recognizes that the client knows about the
server-assigned node UID, the server may remove the mapping for the
temporary node UID.
[0132] At block 910, the routine determines whether the mutation
request violates any conditions of the DDOM locking system. As an
example, an attempt to perform a node insertion on a node that is
locked by another client, may be rejected. If that is the case, the
routine continues at block 918. Otherwise, the routine continues at
block 912. At block 912, the routine determines whether the
requester has sufficient privileges to make the requested mutation.
As an example, the requester may not be able to change an attribute
relating to a node if the user is a member of a privileged group
that only has read access to the node. If the requestor is not
privileged to make the requested mutation, the routine continues at
block 918. Otherwise, the routine continues at block 914, where the
routine determines whether node relationships indicated in the
mutation request remain valid in the master version of the
document. As an example, if the mutation request is to insert a
node relative to a second child of a parent, the routine may
determine whether the indicated child is still a child of the
parent. If the relationship is still valid, the routine continues
at block 916. Otherwise, the routine continues at block 918. At
block 916, the routine returns an indication that the requested
mutation is applicable. At block 918, the routine returns an
indication that the requested mutation is not applicable.
[0133] FIG. 10A illustrates a flow diagram for an embodiment of the
Mutate Request routine. The routine 1000 begins at step 1002, where
it receives an indication of a message containing a requested
mutation as a parameter. At block 1004, the routine determines
whether the received mutate message contains a "Create" request. If
that is the case, the routine continues at block 1006. Otherwise,
the routine continues at block 1008. At block 1006, the routine
assigns a temporary node ID to the newly created node. The
temporary node ID is used by the client in subsequent messages to
or from the server in relation to the newly created node until such
time as the server provides a node UID. After the client receives
the server's node UID, further messages relating to the node use
the new node UID. At block 1008, the routine applies the requested
mutation to the client's local copy of the document and may log the
mutations applied to the local copy of the document in a local
history. The routine may check the local history to determine an
appropriate portion of the client's copy of the document to which
to apply mutations (described further below in relation to FIG.
10B). At block 1010, the routine determines whether the mutation
requires a message to be sent to the server. For example, mutation
requests on DDOM fragments may not need to be sent to the server
(e.g., because the DDOM fragment has not yet been added to the
master version of the document.) If a message needs to be sent to
the server, the routine continues at block 1012. Otherwise, the
routine continues at block 1020. At block 1012, the routine
determines whether the DDOM client is operating in synchronous
invocation mode. If the client is operating in synchronous
invocation mode, the routine continues at block 1014. Otherwise,
the routine may launch a separate thread of execution to continue
at block 1014 and return the present thread to the caller at block
1020. At block 1014, the routine calls the server: Mutate Tree
Subroutine. This subroutine is described above in relation to FIG.
7A. This subroutine is performed at the server. At block 1016, the
routine calls the Client: Apply Mutation Subroutine. This
subroutine is described below in relation to FIG. 10B. At block
1018, the routine determines whether the DDOM client is operating
in synchronous invocation mode. If that is the case, the routine
returns to its caller at block 1020. Otherwise, because another
thread has already returned to the caller after block 1012, the
routine stops performing this thread at block 1022. Thus, under
asychronous invocation mode, a client-side business logic component
may not need to wait for the DDOM client to receive a response from
the server before the routine returns.
[0134] FIG. 10B illustrates a flow diagram for an embodiment of the
Client: apply mutation routine. This routine applies mutations
received in answer and broadcast messages to a client's local copy
of a document. The routine 1050 begins at block 1052 where it
receives an indication of a message containing a requested mutation
as a parameter. This message may be received from a server in
answer to a request from a client that is performing the routine or
as a broadcast message possibly in response to another client's
mutation request. At block 1054, the routine determines whether the
message is an answer message or a broadcast message. If the message
is an answer message, the routine continues at block 1056.
Otherwise, the routine continues at block 1062. At block 1056, the
routine determines whether the answer indicates that a message was
successfully applied at the server. If that is the case, the
routine continues at block 1058. Otherwise, the routine continues
at block 1062. At block 1058, the routine determines whether the
answer is in response to a "Create" request. If that is the case,
the routine continues at block 1060. Otherwise, the routine
continues at block 1062. At block 1060, the routine replaces the
temporarily created local node UID with the server's node UID that
is indicated in the answer.
[0135] At block 1062, the routine generates a pre-application
event. A registered event handler may respond to such an event by
performing activities such as causing further mutations or
performing other client-side work. At block 1064, the routine may
adjust the target location for the received mutation. The routine
may adjust the target location when it is unable to interpret
context information appearing in a message from the server. To
adjust the target location, the routine may consult a local history
of node movements that are results of client-side mutations applied
in local before server tree update mode that are not yet
acknowledged by the server. As an example, an "insert before"
operation referencing a node that the client has moved may be
processed by the client even though the server has neither
processed nor acknowledged the mutation operation on the referenced
node. As a further example, if the mutate message includes an
instruction to insert a node A to the left of node C but the client
has removed node C, the client may consult the local history to
determine that node C previously appeared to the left of node D. As
a result, the client may add node A to the left of node D.
[0136] At block 1066, the routine applies the received mutation on
the client's local copy of the document. Either after blocks 1064
or 1066, the routine may clear information for the target of the
mutation in the local history log and adjust the history log's
records that refer to the target node as its positioning is now
established based on the message from the server. This may be the
same history log that may be used to adjust the target location at
block 1064. The routine returns execution to its caller at block
1070.
[0137] The local history may be used to resolve simultaneous or
independent mutations occuring to related nodes. A client operating
asynchrounously in local before server tree update mode may use the
local history to resolve problems that may occur when the server is
unable to accept the client's mutation request or when the client
receives a conflicting mutation from the server, such as to adjust
the target location for a mutation (e.g., block 1064). As an
example, suppose a document contains a subtree beginning at node R,
which as children X, Y, and Z, and node X has children A, B, and C.
The client may make a local mutation moving node B to become a
child of node Y. Upon making the mutation asynchronously in local
before server tree update mode, the client stores the locally
applied mutation in the local history and sends a mutation request
to the server. Before the server acknowledges the request, the
client may receive a broadcast message from the server indicating
that node Z is to be moved to become a child of node X to the right
of node B. However, because node B is no longer a child of node X
(and is instead a child of node Y), the client detects that the
mutation from the server conflicts with the locally applied
mutation. To resolve the conflict, the client determines from the
local history that node B was previously a child of node X between
nodes A and C. The client then determines that it can satisfy the
mutation from the server by making node Z a child of node X between
nodes A and C.
[0138] The local history comprises mutations initiated by a client.
When a mutation results in the node having a new parent or right
sibbling, aspects of the mutation may be stored in the local
history. For each mutation, the local history may comprise a node
to which the mutation was applied, the node's parent, the next
sibbling to the right of the node, and other history-related
content. When the client receives a mutation from a server
specifiying a parent and right child of a node to which a mutation
is to be applied, the client determines whether the local history
contains an entry for the node. If the local history contains an
entry for the node, the client may transfer the content in the
local history relating to other nodes that have relationships to
the node and removes the entry relating to the node. When a node is
added to the local history, information relating to its right
sibbling is also recorded. When the right sibbling also has an
entry in the local history, the right sibbling's right sibbling is
treated as being the node's right sibbling. The process of adding
information relating to right sibblings may be performed
recursively until no further right sibblings with entries in the
local history are found. In an embodiment, other mutations may also
be stored in the local history. In various embodiments, the left
sibbling may be used instead of the right sibbling.
[0139] The client may process broadcast messages and answer
messages differently. Broadcast messages may be considered to be
directives from the server and may be processed without
consideration as to whether they contradict local changes. Positive
answer messages for node creation requests may require the client
to map the node UID provided by the server to the temporarily
created local node UID.
[0140] FIG. 11 illustrates a flow diagram for an embodiment of the
Receive Message routine. The routine 1100 begins at block 1102,
where it receives an indication of a message as a parameter. A
message may comprise a header and a payload and may include content
in various formats. Message content includes information content
required for mutation requests. Message format is syntax employed
to capture this information. Possible message formats include,
e.g., ASCII, binary, and XML. At block 1104, the routine waits for
the next message. At block 1106, the routine determines whether the
received message is correctly ordered. If the message is correctly
ordered, then all messages are accounted for and the routine
continues at block 1108. Otherwise, the routine requests
retransmission of missing messages from the server at block 1110.
At block 1108, the routine calls the Client: Apply Mutation
routine. A message may have an indication of an ordering. As an
example, the message may contain a sequence number. The routine may
track the sequence numbers of the received messages. If, e.g.,
sequence number 10 is received after sequence number 8, the routine
may recognize that the message was not correctly ordered because
sequence number 9 was missed.
[0141] At block 1110, the routine requests the missing broadcasts.
As an example, the routine may request missing broadcast sequence
number 9 when it receives sequence number 10 after sequence number
8.
[0142] FIG. 12 illustrates a flow diagram for an embodiment the
Roll Forward routine. The routine 1200 begins at block 1202, where
it receives an indication of a requested version of the document.
At block 1204, the routine locates and loads a stored snapshot
version from Version Storage 414 that is near the requested
snapshot version. A snapshot version is nearer to a requested
version than another snapshot version when, e.g., the difference in
time between the specified version and the stored version is lower.
A snapshot version may also be nearer to the requested version when
the mathematical difference between the version numbers is lower.
At block 1206, the routine applies all mutations made to the tree
that were previously stored between the version of the snapshot and
the requested version. As an example, if a requested version is
Sep. 25, 2003, and the nearest snapshot is Aug. 12, 2003, the
system may load the Aug. 12, 2003 snapshot and apply all mutations
made to the tree between Aug. 12, 2003 and Sep. 25, 2003. The
routine ends at block 1208.
[0143] FIG. 13 illustrates a flow diagram for an embodiment the
Roll Back routine. The routine begins at step 1302 where it
receives an indication of a requested version. At block 1304, the
routine locates and loads a stored snapshot from Version Storage
414 that is near the desired version. Determination of proximity of
version numbers is discussed above in relation to FIG. 12. At block
1306, the routine undoes the effects of mutations between the
loaded snapshot and the desired version. The routine ends at block
1308.
[0144] FIG. 14 illustrates a block diagram of an embodiment of a
communications protocol stack used by the system. The stack 1400
includes a DDOM Message Layer 1402. The Message Layer defines
message content and format and may communicate with a Universal
Protocol Layer 1404. The Universal Protocol Layer offers an
abstract interface to the message layer for transmission and
reception of messages. The Universal Protocol Layer interacts with
a number of possible protocol adapters that manage communications
over transport protocols. The illustrated embodiment shows UDP,
TCP, and HTTP. As an example, a UDP protocol adapter 1406 manages
communications over UDP 1407. Similarly, the TCP protocol adapter
1408 manages communications over TCP/IP. Furthermore, the HTTP
protocol adapter 1410 manages communications over HTTP and HTTPS.
The communication system architecture illustrated here can be
extended to support other transport protocols as required. The UDP
and HTTP communication protocols use the IP and TCP/IP protocol
layers, respectively. Other communication protocols may either use
the TCP protocol layer directly or another protocol layer 1414. The
stack presents a session-oriented reliable layer to either a client
DDOM system or a server DDOM system. One skilled in the art will
recognize that a protocol stack may be comprised of individual or
multiple protocol forms.
[0145] FIG. 15 illustrates a block diagram of an embodiment of a
DDOM frame. A DDOM frame 1500 may be comprised of a DDOM frame
header and DDOM frame content. A DDOM frame header may include
multiple fields. One field in the DDOM frame header may be an
indication of a first message identifier in the DDOM content. A
second field in the DDOM frame header may be a last message
identifier in the DDOM content. The first message identifier may
never be larger than the last message identifier. Another field in
the DDOM frame header may be a count of a number of messages in the
DDOM content. Contents of a DDOM frame may be binary-encoded. When
the header data is binary encoded, a standard telecommunication
byte ordering, such as most-significant bits first, may be used.
The DDOM frame content comprises the messages indicated in the DDOM
frame header. The DDOM frame content may also include other
information. Messages in the DDOM frame content may have associated
headers and payloads. Each message may also be identified by a
message identifier. As an example, the DDOM frame header may
contain an indication that the frame covers messages 8 through 12,
and that two messages appear in the frame. A client receiving such
a frame, having previously received upto message 6, would determine
that it is missing message 7. A message payload may contain
mutation-related information.
[0146] FIG. 16 is a block diagram illustrating an embodiment of a
DDOM system call execution pattern when the DDOM system is
operating in a synchronous mode. In this mode, when a client sends
a mutation request to a server, the request is sent as a message to
the DDOM server. Using various rules, the server may determine
whether the mutation is applicable to the document as it presently
exists on the server. If the requested mutations are applicable,
the server may cause the mutations to occur on its master version
of the document. Mutation requests may also be initiated by the
server. For example, a mutation request may be initiated as a
handler's reaction to a mutation request initiated by a client.
Mutations may also be initiated asynchronously by the server in
response to external stimuli. In an attempt to keep documents
consistent across a server's master version and client copies,
clients may process messages from the server in the same sequence
in which the server sends messages.
[0147] FIG. 17 is a block diagram illustrating an embodiment of a
DDOM system call execution pattern in an asynchronous mode. In this
mode, a client sends a mutation request to a server. However, the
client may continue to perform other mutations to its local copy of
the document without receiving an acknowledgment from the server.
Upon receiving a mutation request from a client, the server
determines whether the mutation can be made based on a set of
rules. The server may return an indication of success or failure to
the client. Handlers on the client or the server may cause
additional mutations to occur as a result of the client-initiated
mutation.
[0148] FIG. 18 is a block diagram illustrating an embodiment of a
notification execution pattern of a DDOM system. A DDOM server may
initiate a notification. A DDOM logic layer may cause the mutations
specified in the notification to be made to a DDOM tree describing
the document. Handlers may cause additional mutations to be made to
the document. When a portion of the DDOM tree representing the
document is not currently cached in, the system may have to load
the relevant portion of the tree from storage before implementing
the mutations.
[0149] A client may connect to a server when an author accesses or
manipulates the document. Multiple clients may be connected to the
server simultaneously. Other clients may be connecting or
disconnecting during a given client's connection with the server. A
client may have multiple connections to a server or to multiple
servers simultaneously.
[0150] In some cases, a software application that already accesses
documents using the DOM may be able to use the DDOM system without
modification of the application. In such cases, the DOM-based
mutations are "trapped" and routed via the central or server DDOM
document. As an example, a software developer may add DOM event
handlers to call the appropriate DDOM methods when a DOM-based
mutation occurs. In other cases, the software application itself
may need to be modified to use DDOM. As an example, a scalable
vector graphics ("SVG") editor that does not natively support
mutation events may need to be modified to use DDOM instead of DOM
because mutation event handlers would never be called when no
mutation events are fired. In such a case, calls to a DOM mutation
method would have to be changed to call DDOM instead. One skilled
in the art would know how to make these changes.
[0151] In other cases where the software application was written
using some varieties of scripting languages, a "wrapper object" may
be used that exports a DOM interface but either calls only DDOM to
handle the mutation, or calls DOM and additionally notifies DDOM as
a side effect to propagate mutations to the server or master
document. One skilled in the art will recognize that not every
option listed above is available in every case. As an example, a
compiled executable program may not be able to utilize a wrapper
object unless the wrapper object replaces the object to which the
program refers.
[0152] The DDOM system may be retrofitted to existing software
applications or used with newly created software applications
designed to use DDOM. Use of a software component in a newly
created software application by means of an API is understood in
the art. The following discussion illustrates use of the DDOM in
various retrofit cases. In this discussion, unless otherwise
indicated, a client/server mode and peer-to-peer mode should be
considered to be equally contemplated. Similarly, a server-based
document and a master document handled by a peer are equally
contemplated. A server computer may be a computer system that first
instantiated a DDOM document. Alternatively, a server computer may
be a computer system that stores master documents. Even though an
embodiment is described, other embodiments are also
contemplated.
[0153] From the foregoing, it will be appreciated that although
specific embodiments of the invention have been described herein
for purposes of illustration, various modifications may be made
without deviating from the spirit and scope of the invention. As an
example, various forms of computing devices may be used, including
palmtops, wireless phones, laptops, desktops, minicomputers, and
mainframe computers. The concepts presented herein can be applied
to forms of hierarchical documents other than XML documents. For
example, the concepts may be applied to hierarchical databases.
Accordingly, the invention is not limited except as by the appended
claims.
* * * * *
References