U.S. patent application number 11/556204 was filed with the patent office on 2008-10-23 for methods of object search and recognition.
Invention is credited to Irina Filimonova, Diar Tuganbaev, Konstantin ZUEV.
Application Number | 20080263021 11/556204 |
Document ID | / |
Family ID | 39360877 |
Filed Date | 2008-10-23 |
United States Patent
Application |
20080263021 |
Kind Code |
A1 |
ZUEV; Konstantin ; et
al. |
October 23, 2008 |
Methods of object search and recognition
Abstract
The proposed technical solution allows processing of
machine-readable forms of unfixed format. An auxiliary brief
description may be optionally specified to determine the spatial
orientation of the image. A method of searching for elements of a
document comprises the following main operations in addition to the
operations of preliminary image processing: selecting the varieties
of structural description from several available variants,
determining the orientation of the image, selecting the text
objects, where the text must be recognized, and determining the
minimal required volume of recognition, recognizing the text
objects, searching for elements of the form. Searching for elements
of the form comprises the following actions: selecting a searched
element in the structural description, gaining the algorithm of
search constraints from the structural description, searching for
the element, testing the obtained variants.
Inventors: |
ZUEV; Konstantin; (Moscow,
RU) ; Tuganbaev; Diar; (Moscow, RU) ;
Filimonova; Irina; (Moscow, RU) |
Correspondence
Address: |
ABBYY Software Ltd.;Attn. Sergey Platonov
11-1, KASATKINA STR., P.O. Box #54
MOSCOW
129301
RU
|
Family ID: |
39360877 |
Appl. No.: |
11/556204 |
Filed: |
November 3, 2006 |
Current U.S.
Class: |
1/1 ;
707/999.005; 707/E17.011; 707/E17.017 |
Current CPC
Class: |
G06F 16/9024
20190101 |
Class at
Publication: |
707/5 ;
707/E17.017 |
International
Class: |
G06F 7/06 20060101
G06F007/06; G06F 17/30 20060101 G06F017/30 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 25, 2006 |
RU |
2006101908 A1 |
Claims
1. A method of searching for element of a document, comprising at
least the following operations of preliminary image processing:
searching for objects on the image; allocating the obtained
objects; selecting the text objects, where the text must be
recognized, and determining the minimal required volume of
recognition. recognizing the text objects; then the program
searches for elements of the form. The search comprises at least
the following actions: selecting a searched element in the
structural description; gaining the algorithm of obtaining the
search constraints from the structural description; searching for
the element; testing the obtained variants; optimizing the analysis
of variants of combinations of elements, and searching for an
element comprises the following operations: searching with the use
of the spatial characteristics of the search area; searching with
the use of the parametric characteristics of the element; searching
with use of the absolute and/or relative spatial characteristics of
the element--represented as exact values and/or as intervals;
searching with the use of the results of preliminary text
recognition, and testing of the obtained elements comprises the
following actions: identifying the obtained variant of the element;
estimating the quality of the identification of the element;
analyzing the results of testing the hypotheses about the presence,
completeness of composition, and types of composite parts,
analyzing their correspondence to the hypothesis about the type in
the case of a compound element; estimating the total reliability of
the obtained variant, optimization of the analysis of variants of
combinations of elements, comprising: assigning a number of
variants with the best quality ratings which will be kept for
further analysis to each type of the element; searching for the
best variant of the compound element, taking into account the best
total quality of its accountable composite parts, regardless of
their number, analyzing the quality estimates of earlier rejected
variants in order to obtain quality estimates higher than the
current estimate. and optimization of the analysis of variants of
combinations of elements comprises the following actions: assigning
a number of variants with the best quality ratings which will be
kept for further analysis to each type of the element; discarding
the other variants; searching for the best variant of the compound
element, taking into account the best total quality of its
accountable composite parts, regardless of their number, analyzing
the quality estimates of earlier rejected variants in order to
obtain quality estimates higher than the current estimate.
2. A method of searching, as recited in claim 1, where the
orientation of the image is determined.
3. A method of searching, as recited in claim 2, where all or a
part of elements of the structural description are used to
determine the correct orientation of the image.
4. A method of searching, as recited in claim 3, where an auxiliary
description in brief form is optionally assigned to determine the
spatial orientation of the image.
5. A method of searching, as recited in claim 3, where the
orientation of the image whose objects of the description coincide
with the objects on the image with the maximal quality rating is
accepted as the correct orientation of the image.
6. A method of searching, as recited in claim 1, where the type of
a document is selected from several available types.
7. A method of searching, as recited in claim 6, where a separate
brief structural description is optionally included for determining
the document type and selecting the corresponding comprehensive
document description from several available descriptions.
8. A method of searching, as recited in claim 7, where the type of
the document which corresponds to the current image is selected on
the basis of comparing the quality estimates of the used
descriptions.
9. A method of searching for an element, comprising at least the
following operations of preliminary image processing: searching for
the object on the image; allocating the obtained objects
classifying the objects according to their types; selecting the
text objects, where the text must be recognized, and determining
the minimal required volume of recognition; recognizing the text
objects; then the program searches for elements of the form. This
search comprises at least the following actions: selecting a
searched element in the structural description; gaining the
algorithm of obtaining the search constraints; searching for the
element; testing the obtained variants; and searching for an
element comprises the following operations: searching with the use
of the spatial characteristics of the search area; searching with
the use of the parametric characteristics of the element; searching
with the use of the spatial characteristics of the element and
testing the obtained elements comprises the following actions:
identifying the obtained elements; analyzing the results of testing
the hypotheses about the presence and completeness of composition
of the elements, and the types of the composite parts, analyzing
the correspondence to the hypothesis about the composition of the
compound element. optimization of the analysis of variants of
combinations of elements comprising: assigning a number of variants
with the best quality ratings which will be kept for further
analysis to each type of the element; searching for the best
variant of the compound element, taking into account the best total
quality of its accountable composite parts, regardless of their
number, analyzing the quality estimates of earlier rejected
variants in order to obtain quality estimates higher than the
current estimate.
10. A method of searching, as recited in claims 1 or 9, where
initially the first element in the list is selected.
11. A method of searching, as recited in claims 1 or 9, where the
spatial characteristics of an element including its absolute
coordinates and/or relative coordinates are used.
12. A method of searching, as recited in claims 1 or 9, where the
exact and/or interval characteristics of an element are used.
13. A method of searching, as recited in claims 1 or 9, where the
following spatial characteristics of the search area are also used:
a half plane, a rectangle, a circle, a polygon, or a combination
thereof.
14. A method of searching, as recited in claims 1 or 9, where the
quality estimates of all earlier rejected variants are analyzed
after the estimation of the total quality rating of the variant to
select a variant with the best quality rating.
15. A method of searching, as recited in claims 1 or 9, where
searching for the next object is performed if there are no variants
for the current element or the total quality rating is lower than
the predefined level.
16. A method of searching, as recited in claims 1 or 9, where
revision of variants of combinations of the elements is considered
complete if the total quality estimate of the complete set of
elements achieves the quality value of 1.
17. A method of searching, as recited in claims 1 or 9, where one
to three variants of a compound element which have the best quality
estimate are used for further analysis.
18. A method of searching, as recited in claims 1 or 9, where three
to ten variants of a simple element which have the best quality
estimate are used for further analysis.
19. A method of searching, as recited in claims 1 or 9, where the
program starts searching for an object corresponding to the next
element of the structural description, if no objects are detected
in the region of the image which is specified for the current
element.
20. A method of searching, as recited in claim 9, where the
orientation of the image is determined.
21. A method of searching, as recited in claim 20, where all or a
part of elements of the structural description are used to
determine the correct orientation of the image.
22. A method of searching, as recited in claim 21, where an
auxiliary brief description is optionally specified to determine
the spatial orientation of the image.
23. A method of searching, as recited in claim 21, where the
orientation of the image whose objects of the description coincide
with the objects on the image with the maximal quality rating is
accepted as the correct orientation of the image.
24. A method of searching, as recited in claims 1 or 9, where the
type of the document is selected from several available types.
25. A method of searching, as recited in claim 24, where a separate
brief structural description is optionally included for determining
the document type and selecting the corresponding comprehensive
document description from several available descriptions.
26. A method of searching, as recited in claim 25, where the type
of the document which corresponds to the current image is selected
on the basis of comparing the quality estimates of the used
descriptions.
Description
[0001] The present invention relates generally to image recognition
and particularly to the recognition of non-text and/or text objects
contained in a bit-mapped image of a document.
[0002] The mentioned methods are also applied for, but not limited
to, recognition of data input forms, containing typographical and
hand-written texts as well as a set of special text-marks for
document navigation. Documents as supposed herein are inquiry
lists, questionnaires, bank documents with rigid or arbitrary
arrangement of data fields.
[0003] The mentioned methods may be applied for recognition of
predefined form objects contained in an electronic graphical
image.
PRIOR ART
[0004] Methods of structure assignment and document element search
in an electronic graphical image are known in the art (U.S. Pat.
No. 5,416,849 Huang, May 16, 1995).
[0005] The capability of the known methods to process only fixed
forms, not allowing deviations in field arrangement, is the
shortcoming of the methods.
[0006] Anyone of the described methods and the system may be taken
as a prototype.
[0007] The technical result consists in the improvement of
searching capabilities as well as the accuracy of identification of
obtained image objects, the increase of noise immunity during the
process of object search on the image.
SUMMARY OF THE INVENTION
[0008] The declared technical result is achieved by using tools for
search and identification of objects on an image; with further
assignment of the estimate of correspondence of the search result
to the description. Numbers from 0 to 1 are used for the
evaluation. The accuracy of evaluation is 10.sup.-5 (ten to the
power of minus five). The value equal to 1 means the absolute
correspondence of the obtained result to the description. If the
estimate differs from zero, the application of flexible structural
description also comprises the stage of forming block regions, i.e.
evaluation of the arrangement of the required fields on the basis
of the information about the obtained objects.
[0009] Structural description comprises the description of spatial
and parametric characteristics of document elements, and the
logical connections between document elements.
[0010] The method of preliminary assignment of a document structure
consists in setting a description of the document's logical
structure in the form of interdependences of spatial and parametric
characteristics of elements, algorithms of obtaining the parameters
of the search for each element, methods of identifying the obtained
elements, methods of decreasing the number of obtained variants of
an element, acceleration of the search for the best variant.
[0011] The method of searching and recognizing the elements (fields
or field fragments) of a document on a graphical (bit-mapped) image
consists in using of a predefined logical structure of the document
in the form of structural description, algorithms of obtaining the
parameters of the search for each element, methods of identifying
the obtained elements, methods of decreasing the number of obtained
variants of an element, acceleration of the search for the best
variant.
[0012] Searching for elements with the help of a flexible
structural description is performed sequentially in the order in
which they are described in the flexible structural description,
top-down through the "tree" (hierarchy) of elements, in accordance
with the logical structure of the document description. For each
element in the assigned search area, several variants of image
objects or sets of image objects corresponding to the description
of the element in the structural description may be found. Various
obtained variants of objects are considered to be the variants of
the position of the element on the image. An estimate of the degree
of correspondence of the variant to the element description is
assigned to each obtained variant (i.e. the estimate of the quality
of the variant).
[0013] The accuracy of the obtained position of the object
determines the accuracy of obtaining the positions of objects
described further in the description relative to this object.
Searching for the next dependent object is performed separately for
each obtained variant of the current object. Therefore, the
variants of objects obtained on the image comprise a hierarchical
tree, considerable more branched than the hierarchical tree of
elements in a structural description.
[0014] If an element or an object is compound, i.e. composed of
several parts, the whole group also represents an element, which
requires generating several possible variants, the number of which
corresponds to the number of complete chains of group sub-elements
(dependent elements of a lower level). The chain is considered
complete if all its obtained sub-elements (elements of a lower
level) have sufficient quality. The total estimate of the quality
of a variant of a compound element is calculated by multiplying the
estimates of the quality of element variants forming the compound
element. A flexible structural description as a whole also
represents a compound element, therefore, the quality of the
correspondence of the variant to the flexible structural
description is determined by multiplying the quality of its
elements.
[0015] Application of a flexible structural description comprises
searching for the best complete branch in the whole tree of
variants, i.e. the branch that include all the elements, from first
to last. A general solution of such a task implies taking into
consideration all the possible combinations of hypotheses for all
elements, construction of a total multitude of complete branches
and selecting the best among them. However, in practice, such a
solution requires too much resources, and is therefore impractical.
Moreover, an abrupt increase in the number of variants taken into
consideration is possible, caused by an increase in the number of
elements and a lack of rigid restrictions on the search area and
element parameters.
[0016] To limit the time required to analyze the variants, one of
the several methods of decreasing the volume is used.
[0017] Each element gets the maximum allowed number of acceptable
variants, rated in the order of decreasing quality. These variants
will be used in the further search, i.e. when searching for the
next element. Any variants beyond this number will be discarded.
Usually this number is 5 (five) for simple elements and 1 (one) for
compound elements. This means that, if 15 variants are obtained for
a simple element in the assigned search area, five variants with
the best quality rating will be selected. Other 10 chains of
variants will not be complete and will not be taken into
consideration. A compound element is identified with a greater
quality rating than a simple element, because the quality of
identification is determined not only by multiplying the quality
ratings of the constituent simple elements, but also by several
additional (mainly qualitative) characteristics, such as mutual
arrangement, object size, correspondence to the conditions of
mutual arrangement several elements, and so on.
[0018] Since a compound element is identified with a greater
quality rating than a simple element, its best variant usually
turns out to be accurate.
[0019] The process of searching for objects almost always includes
generating several incomplete chains of variants of obtained
objects and, therefore, several directions of further search.
Search for the best hypothesis is performed by using an algorithm
of "broad searching", i.e. the search is always directed through
the chain of variants which has the best quality rating at the
current step, regardless of the length of the chain. For example,
if in a flexible structural description of 30 elements 2 chains are
obtained during search, one of which consists of 30 elements with
the quality rating of 0.89 and the other chain has 2 elements with
the quality rating of 0.92, then the second chain will be pursued
until its total quality becomes lower than that of the first
chain.
[0020] The following rule of quality optimization is used for
compound elements: if an ideal complete chain for this element is
obtained, i.e. the quality of the obtained chain equals 1, other
variants of sub-elements composition of this compound element are
not taken into consideration.
[0021] Moreover, the maximum number of variants for every element
in the entire hypothesis tree is restricted to 1000.
DETAILED DESCRIPTION OF THE INVENTION
[0022] A set of spatial and parametric characteristics sufficient
for search for and identification of an element is used to describe
elements of a document of anon-fixed format. A structural
description consists of a description of spatial and/or parametric
characteristics of the element, and a description of its logical
connections with other elements.
[0023] A flexible structural description may also additionally
include all or some of the following conditions. The logical
structure of a document is represented as a sequence of elements
connected mainly by hierarchical dependences; an algorithm of
determining the search parameters is set, spatial characteristics
for searching for each element are specified, parametric
characteristics of the searching for each element are set, the set
of parameters for identifying a compound element on the basis of
the aggregate of components is set, and an algorithm of estimating
the quality of an obtained variant of an element is set.
[0024] A flexible structural description may also additionally
include a separate brief structural description for determining the
correct spatial orientation of the image.
[0025] A flexible structural description may also additionally
include a separate brief structural description for determining the
document type and selecting the corresponding comprehensive
document description from several possible descriptions. A
comprehensive description is created for each document type. If a
document type does not have a brief description, then the
comprehensive description of the document is used for selecting its
type.
[0026] The structure of element connection is mainly realized as a
hierarchical structure.
[0027] The essence of the invention as regards the method of
searching (recognizing) elements (fields) on a document form in a
bit-mapped image according to the first method consists in the
following. A method of searching and identifying (including
recognition) the elements of a document with non-fixed format
comprises at least the following preliminary actions. Revision of
the whole document image. Detection of obtained objects or object
fragments. Performing an initial classification of detected objects
according to the set of predefined types. Recognition of all or a
part of text objects, where each object is recognized partially or
entirely. To speed up the processing, recognition of text objects
is performed to a degree which is sufficient for identifying the
document structure and other elements of the form.
[0028] A separate structural description is set to detect the
spatial orientation of an object. Such a description usually
contains a brief set of structural elements which can be easily
recognized on a document (form). Orientation is accepted as correct
if the elements of the structural description coincide with the
elements on the image with the best quality estimate.
[0029] A corresponding separate brief description is set for quick
detection of the type of recognized document and selecting the
comprehensive (main) description of the document type from several
possible descriptions. A comprehensive description is created for
each document type. If any document type does not have a brief
description, then the comprehensive description of the document is
used for selecting its type, and the selection of the document type
is performed by comparing the quality estimates of the used (brief
or comprehensive) descriptions of different types.
[0030] Then the following main actions are performed. Choosing an
element for search in the structural description. Obtaining an
algorithm of determining the search parameters from the structural
description. Searching for the element. Testing the obtained
variants.
[0031] Searching for an element comprises the following operations.
Search by using the spatial characteristics of the search area (for
example, a half-plane, a rectangle, a circle, a polygon, or any
combinations thereof). Searching by using parametric
characteristics of an element. Search by using the spatial
characteristics of an element. For example, as absolute coordinates
and/or coordinates relative to the other elements (located higher
in the tree). The coordinates may be specified as exact values or
as an interval.
[0032] Search with the help of the results of preliminary text
recognition.
[0033] Testing the detected elements comprises the following
actions. Identification of detected elements. Analysis of the
results of testing the hypotheses about the presence of the
element, completeness of the element composition, and types of
composite parts of the element, analysis of correspondence of the
structure of a compound element to the hypothesis.
[0034] Optimization of the search through element combination
variants, in its turn, comprises the following actions. Assigning
to each element several variants with the best quality rating,
which are kept for further analysis, and discarding all other
variants. Searching for the best variant of a compound element,
taking into account the best total quality estimate of the
composite parts, regardless of their number. The total quality
estimate of a compound element is calculated as the product of the
quality estimates of the parts thereof. Additionally, other
qualitative characteristics are taken into consideration.
[0035] Initially, the first element in the list is selected.
[0036] The following spatial characteristics of an element may be
also applied: absolute coordinates and/or coordinates relative to
the other elements.
[0037] The coordinates may be specified as exact values or as an
interval.
[0038] The following spatial characteristics of the search area may
be used: half-plane, rectangle, circle, polygon.
[0039] Revision of the element combination variants is considered
complete if the total quality estimate of the complete set of
elements achieves the quality value of 1.
[0040] The number of variants of a compound element which have the
best quality estimate and are used for further analysis should be
in the range from one to three.
[0041] The number of variants of a simple element which have the
best quality estimate and are used for further analysis should be
in the range from three to ten.
[0042] A method of search and recognition (identification) of
elements (fields) on a document of non-fixed format according to
the second variant comprises at least the following preliminary
actions. Revision of the entire document image. Allocation of the
detected objects or object fragments. Performing the initial
classification of the allocated objects according to the set of
predefined types. Recognition of all or a part of text objects,
where each object is recognized partially or entirely. Recognition
of text objects is performed to a degree which is sufficient for
identifying the document structure and other elements of the
form.
[0043] A separate structural description is set to detect the
spatial orientation of an object. Such a description usually
contains a brief set of structural elements which can be easily
recognized on a document (form). Orientation is accepted as correct
if the elements of the structural description coincide with the
elements on the image with the best quality estimate.
[0044] A corresponding separate brief description is set for quick
detection of the type of a recognized document and selecting the
comprehensive (main) description of the document type from several
possible descriptions. A comprehensive description is created for
each document type. If any document type does not have a brief
description, then the comprehensive description of the document is
used for selecting its type, and the selection of the document type
is performed by comparing the quality estimates of the used (brief
or comprehensive) descriptions of different types.
[0045] Then all or at least a part of the following operations are
performed.
[0046] Choosing the next element in the structural description
(starting from the first one).
[0047] Calculating or getting a predefined algorithm for
determining the search parameters.
[0048] Performing a search for an element, comprising at least the
following operations:
[0049] searching by using the spatial characteristics of the search
area such as, for example, half-plane, rectangle, circle, polygon
and others;
[0050] searching by using the parametric characteristics of an
element (the type of element);
[0051] searching by using the spatial characteristics of an
element, represented as absolute coordinates and/or coordinates
relative to the other elements.
[0052] The coordinates may be specified as exact values or as an
interval.
[0053] calculating the quality of correspondence of the obtained
variant to the description of the required element.
[0054] Testing the obtained variant of the object comprises the
following operations.
[0055] identifying the obtained element variant;
[0056] calculating the quality of the identification of the
element;
[0057] analyzing the results of testing the hypotheses about the
presence and completeness of the composition of the element and the
types of composite parts, analyzing of the correspondence of a
compound element to the hypothesis about the type of the
element;
[0058] calculating the total reliability of the obtained
variant
[0059] Optimization of revision of element combination variants
comprises
[0060] assigning to each type of the element several variants with
the best quality rating, which are kept for further analysis;
[0061] searching for the best variant of a compound element, taking
into account the best total quality estimate of composite parts,
regardless of their number.
[0062] revision of the quality estimates of the variants which were
discarded earlier in order to find any quality estimates which
would be higher than the current one.
[0063] If the total quality estimate is lower than the predefined
level, searching for the next variant of the same element and
calculating its total quality estimate are performed.
[0064] If the total quality estimate is higher than the predefined
level, searching for the next element is performed.
[0065] The variant with the maximum total quality estimate is
selected.
[0066] Searching for the best variant of a compound element is
performed, taking into account the best total quality estimate of
accountable composite parts, regardless of their number.
[0067] The quality of a variant as supposed herein is the
estimation which indicates the degree of correspondence of the
obtained variant to the present element (its properties and search
constraints). The numerical constituent of the quality of a variant
is a number ranging from 0 to 1. The quality of a hypothesis for a
compound element is calculated by multiplying the quality estimates
of the hypotheses of all the sub-elements thereof.
[0068] The quality of a variant is a result of multiplication of
the quality of the element, assigned at the stage of specification
of the structural description during the specification of the
element type, and the quality of the element (object), variant is
calculated at the stage of the search. The total quality of the
variant is calculated as a product of quality ratings of all
interdependent composing elements in the chain, from the first
element in the structural description to the current element.
[0069] For optional elements i.e. such elements, which may be
missing on a document, a "zero" variant of an element is used, if
the element has not been detected. A "zero" variant supposes that
the required object is missing in the search area. A "zero" variant
is formed, if no objects are detected corresponding to the optional
element and having the quality estimate which is greater than the
quality of the zero variant. If the zero variant is selected as the
most appropriate, the process is started of searching and
identifying the next element in the list (including the elements
which depend on the element which has not been obtained), or
analyzing one of the earlier rejected variants of the same element
or another element, simultaneously taking appropriate measures to
avoid creating an infinite loop in the process.
[0070] If no objects are detected corresponding to the optional
element, the use of the flexible description is not stopped.
Instead, a zero variant is generated which gains the quality value
predefined by the user in the description of this optional
element.
[0071] Creation of the flexible structural description uses the
following main types of elements conventionally divided into the
following: simple element which do not contain other elements:
Static Text, Separator, White field, Barcode, Text String, Text
Fragment, Set of objects, Date, Phone Number, Currency, and Table,
and compound elements--Group, and some other types.
[0072] Static text, as supposed herein, is an element of structural
description describing a text with the known meaning. The text may
consist of one word, of several words, or of an entire paragraph.
"Several words" differs from "a word" by the presence of at least
one blank space or another inter-word separator, depending on the
language, for example, a full stop, a comma, a colon, or any other
punctuation mark. Several words may take up several text
strings.
[0073] Separator, as supposed herein, is an element representing a
vertical or horizontal graphical object between other objects. A
separator can be represented, for example, by a solid line or a
dotted line.
[0074] White field, as supposed herein, is an element of
description representing a rectangular region of an image which
does not contain any objects within it.
[0075] Barcode, as supposed herein, is an element of flexible
description representing a line drawing which codes numerical
information.
[0076] Text string, as supposed herein, is an element representing
a sequence of characters located on a single line one after
another. Character strings can consist of text objects, for
example, words, or of fragments of text objects.
[0077] Text fragment, as supposed herein, is an element
representing an aggregate of text objects.
[0078] Set of objects (of the specified type), as supposed herein,
is an element representing an aggregate of different types of
objects on an image, where each object meets the search
constraints.
[0079] Date as supposed herein, is an element representing a
date.
[0080] Telephone number, as supposed herein, is an element
representing a telephone number which may be accompanied a by
prefix ("tel.", "home tel.", etc.) and by a code of the
city/region, which is separated from the number by brackets.
[0081] Currency, as supposed herein, is an element of description
representing money sums, where the name of the currency can be used
as the prefix.
[0082] Table, as supposed herein, is an element of flexible
description representing data in the form of a table.
[0083] Compound element (element group), as supposed herein, is an
aggregate of several elements (sub-elements). Sub-elements may be
simple or compound.
[0084] Compound elements are used for:
[0085] joining elements into a group. Each of these compound
elements may contain smaller compound elements which search for
smaller fragments of the element;
[0086] providing the logical hierarchy of elements for better
navigation through the structural description;
[0087] reducing the number of possible variants of the element in
order to speed up the search for the resulting variant. Joining
elements into a compound element allows to analyze this set of
sub-elements as a single entity which has its own complete variant
(consisting of the variants of the sub-elements) and a total
estimate of reliability of the entire group. Revision of possible
combinations of variants of the sub-elements is performed within
the group, and only a predefined number of the best variants in the
group take part in the further analysis and search for the next
elements. The number of the best variants of a compound element
which take part in further searching is usually 1;
[0088] specifying restrictions of the search area which are common
for all the sub-elements. The search area of a certain sub-element
in this case is calculated as the intersection of the search area
set for the sub-element itself and the search area of the group
which contains this sub-element.
* * * * *