Abstract:
An improved system for determining compliance between a source document structure in accordance with a source schema and a target schema includes: data storage; and a processor for executing software code. The software code causes the processor to: create a source schema description and a target schema description; receive the source document which includes an ordered tree structure with labeled elements and including a subtree; identify all corresponding element types in the source and target schemas for grouping the corresponding element types into element type pairs; classify each element type pair; and confirm compliance of the source document.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of commonly-owned, U.S. application Ser. No. 10/662,799, filed on Sep. 12, 2003 now U.S. Pat. No. 7,596,748, which application is herein incorporated by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED-RESEARCH OR DEVELOPMENT 
     None. 
     INCORPORATION BY REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
     None 
     FIELD OF THE INVENTION 
     The invention disclosed broadly relates to the field of data and document management software. More particularly, the present invention relates to an improved method of determining, in a manner that requires less processing time than prior art methods, whether a set of XML or text documents, known to conform to a first schema, are valid with respect to a second schema. 
     BACKGROUND OF THE INVENTION 
     To ensure that data satisfy certain structural and non-structural constraints, it is common to use a schema, or data model, which provides a template for the data or document. One common representation for data is the Extensible Markup Language, or XML, which comprises a simplified subset of the Standardized Generalized Markup Language, or SGML. Unlike other subsets of SGML such as the Hypertext Markup Language (HTML), XML permits users to define new element labels and to nest XML elements within one another. Generally, schemas are used to constrain what labeled elements may appear in an XML document and how they may be arranged; an XML document conforms to a schema if the structure of the document satisfies the constraints specified by the schema. A schema for an XML document is built up out of type definitions. Together, the type definitions specify constraints on the structure of elements in an XML document such as, for example, the attributes that elements in the document may contain, the mandatory or optional nature of the elements, and the order in which the elements appear, and what other elements may be nested within an element. 
     One basic schema specification standard for XML is the DTD (Document Type Definition). In many XML applications, there is a DTD definition that specifies the XML format and one or more XML documents that conform to the DTD. Another common formalism for specifying the format of XML documents and data is the XML Schema. An XML Schema definition sets forth the layout format of documents that conform to the schema. This layout format includes which elements appear in each document and the data type for each element (such as whether it is numeric, binary, character, image, etc.). In addition, the XML Schema definition or DTD definition may include relational information that specifies how the various elements in conforming documents are related to each other. For example, for data that has a hierarchical structure, parent and child relationships will be described in the schema. 
     More generally, schemas may be any of a DTD, an XML Schema, or a string specification schema (such as a regular expression, a grammar or a finite state automaton), and documents may be either an XML document or a string. 
     Often documents or data objects that conform to a particular schema need to be verified as conforming with (i.e. recast into) another schema. For example, a business may have been saving and processing its customer records in accordance with a particular schema. However, the business may now desire to store its records in accordance with a new schema. In order to insure compatibility between its old and new records, the business may desire to recast the prior records into the new schema. As a further example, a program that processes documents typically expects to receive the documents in a particular format. If a business desires to process certain documents that are structured in accordance with a different schema with the program, it may be necessary to recast the documents into the appropriate schema. 
     Unfortunately, it is sometimes impossible to cast a particular document from one schema into another schema. For instance, the new schema may require a nonzero value for a particular element that is not present in the document in the first schema. Thus, in order to cast a document into a new schema, the document in the first schema must be valid in the second schema. The prior art method of validating a document in a schema is to examine each element that is going to be cast in the schema to determine if it is valid in the schema. Since businesses often have voluminous records, examining each individual element of each document in a particular schema to determine if it will be valid in a second schema can be a very time consuming process. Therefore, what is needed is an improved method of determining whether or not a document is valid with respect to a particular schema given that it conforms to another schema. 
     SUMMARY OF THE INVENTION 
     A preferred application (henceforth referred to as Application 1) of the present invention is directed towards a system for validating a document structured as an ordered tree having labeled elements, known to conform to varying element types in accordance with a first schema, with respect to a second schema. The method includes preprocessing the first and second schemas to identify subsumed type-pairs, of the form type 1 -type 2  where type 1  is a type defined in the first schema and type 2  is a type defined in the second schema. Such a pair indicates that an element&#39;s content that conforms to the first type, type 1 , will also conform to the second type, type 2 . For XML Schema, the method includes identifying subsumed element tag-type-pairs, of the form tag-type 1 -type 2 , where tag is an element name, type 1  is a type in the first XML Schema and type  2  is a type in the second XML Schema; it indicates that if the specified element tag appears in a document conforming to the first schema with content of type 1 , then this element tag can validly appear in a document conforming to the second schema and its content will conform to type type 2 . Similarly, disjointed type-pairs and disjoint element tag-type-pairs are also identified. Disjoint type 1 -type 2  where type 1  is defined in the first schema and type 2  is defined in the second schema, indicates that no content that conforms to type 1  can also conform to type 2 . Disjoint tag-type 1 -type 2  indicates that if the specified element tag appears in a document conforming to the first schema with content of type 1 , then this element tag cannot appear in a document conforming to the second schema where to be valid its content must conform to type type 2 . If a type-pair, or element tag-type-pair, is neither subsumed nor disjoint, it is called intersecting. Intuitively, intersecting means “sometimes valid in the second schema”. 
     A document known to conform to the first schema is immediately validated for the second schema only if all element tag-type-pairs in the first schema that can apply to root nodes of the document are subsumed by all element tag-type-pairs in the second schema that can apply to root nodes of the document. A document is immediately invalidated in the second schema if all such element tag-type-pairs are of the disjoint kind. Otherwise, portions of the document need be examined as we now describe. The topmost element of the document is examined and its tag and type according to the first schema, type 1 , is either determined or read (if stored). The type type 2  according to the second schema is determined by examining the schema. If tag-type 1 -type 2  is a subsumed element tag-type-pair the document is validated according to the second schema. Otherwise, if tag-type 1 -type 2  is disjoint, or if type 1 -type 2  is disjoint, then the document is immediately invalidated. Otherwise, the tags of the children of the top element are examined. If it is determined that they cannot possibly conform to type 2  (that part is called “content model verification”) the document is invalidated according to the second schema. Since the validation process with respect to the second schema can stop with a validation or invalidation after only part of the document has been explored, due to types being disjoint or subsumed appropriately, there is significant gain to the state of the art where the whole document must necessarily be processed. 
     Another application (henceforth referred to as Application 2) of the present invention is directed toward a system for determining whether or not a string data set conforming to a first string schema can be cast in a second string schema without validating all of the data set in accordance with the second schema. The method includes checking whether the schema-pair schema 1 -schema 2  is subsumed (i.e., any string conforming to the first schema also conforms to the second schema), is disjoint (i.e., no string conforming to the first schema can conform to the second schema), or otherwise intersecting. The method includes checking if the schema-pair schema 1 -schema 2  is subsumed, and if so validating it immediately. The method also includes checking if schema 1 -schema 2  is disjoint, and if so invalidating it immediately. If the pair schema 1 -schema 2  is intersecting, an automaton (a simple computation device) is constructed out of the pair schema 1 -schema 2 . The automaton needs only examine the relevant portions of the document to determine whether the document conforms to schema 2 . Such an automaton is called “an immediate decision automaton”. Interestingly, such automata can greatly enhance computational efficiency if used in the “content model verification” of the previous method. This will be further explained later on. 
     Yet another application (henceforth referred to as Application 3) of the present invention is directed toward a system for determining whether a document conforming to a first DTD schema may be cast in a second DTD schema without validating certain portions of the document in accordance with the second schema by comparing the first schema and the second schema. The method involves first checking whether every element tag-type-pair that can apply to root nodes of a document is subsumed and if so we have validation according to the second schema. Observe that for DTDs, for each tag there is at most one type in the first schema and at most one type in the second schema. Otherwise, one can invalidate the document immediately with respect to the second schema if every element tag-type-pair that can apply to root nodes of a document is disjoint. Otherwise, if there is an occurrence of a tag-type 1  combination in the document such that tag-type 1 -type 2  is disjoint, the document is invalidated according to the second schema. Otherwise, all occurrences of element tags, tag, such that tag-type 1 -type 2  is intersecting are checked to verify that their content model is according to type 2 . If so, the document is validated, and otherwise invalidated, according to the second schema. These occurrences may be accessed directly, if a mechanism enabling this exists; otherwise, the document is processed recursively as in the case of the method for XML Schemas we have previously described. In checking these occurrences, the method of Application 2 (strings) may be used in verifying content models. 
     Yet another application (henceforth referred to as Application 4) of the present invention is directed toward a system for determining whether a document, whose original version (henceforth referred to as the original) prior to applied modifications conforms to a first schema, can be checked for conformance to a second schema without validating every element of the document. Modifications include any sequence consisting of or having the effect of changing the tag of an element, inserting a new leaf node at a specified location, or deleting a specified leaf node. The method utilizes knowledge as to which subtrees contain new or modified content, and which have their original document content, to examine only relevant portions of the document. In this method, new portions need to be verified for conformance to the second schema, whereas for unmodified subtrees (that may be contained within modified subtrees) the method of Application 1 and Application 2 may be used to further limit the computational effort. 
     Yet another application (henceforth referred to as Application 5) of the present invention is directed toward a system for determining whether or not a string data set, whose original version (henceforth referred to as the original) prior to applied modifications conforms to a first string schema can be cast in a second string schema without validating all the data set in accordance with the second schema. The method includes the construction of an immediate decision automaton for the second schema and an immediate decision automaton based on both schemas. The first automaton is used over the leftmost part of the document, up to a point beyond which there are no modifications. In so doing, it may accept (respectively, reject) that is validate (respectively, invalidate) according to the second schema. If no decision is reached, the automaton based on both schemas is used thereafter. Here too there are great potential savings as compared with the state of the art method of rechecking. This method is also useful within Application 4 in verifying content models. 
     Yet another application (henceforth referred to as Application 6) of the present invention is directed toward a system for determining whether a document, whose original version (henceforth referred to as the original) prior to applied modifications conforms to a first DTD schema may be cast in a second DTD schema without validating certain portions of the document in accordance with the second schema by comparing the first schema and the second schema. This method is further described in the detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1(   a ) and ( b ) show an exemplary source and target XML schema; 
         FIG. 2  is an illustration of a preferred method for determining whether a document that is valid in a first schema is valid in a second schema in accordance with an embodiment of the present invention (Application 1); 
         FIG. 3 , is an illustration of a preferred method for determining whether a string document that is valid in a first string schema is valid in a second string schema in accordance with an embodiment of the present invention (Application 2); 
         FIG. 4 , is an illustration of a preferred method for determining whether a document that is valid with respect to a first DTD schema is valid with respect to a second DTD schema in accordance with an embodiment of the present invention (Application 3); 
         FIG. 5  is an illustration of a preferred method of casting a document that was valid in a first schema prior to being modified into a second schema in accordance with an embodiment of the present invention (Application 4); 
         FIG. 6  is an illustration of a preferred method of casting a string document that was valid in a first string schema prior to being modified into a second string schema in accordance with an embodiment of the present invention (Application 5); 
         FIG. 7  is an illustration of a preferred method of casting a document that was valid in a first DTD schema prior to being modified into a second DTD schema in accordance with an embodiment of the present invention (Application 6); and 
         FIG. 8  is an illustration of an information handling system constructed in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to  FIGS. 1(   a ) and  1 ( b ), exemplary fragments of a first XML schema or document structure and a second XML schema are shown. The first and second schemas both have element type declarations for the element “purchaseOrder”. The only difference between the schema of  FIGS. 1  ( a ) and ( b ) is that the “billTo” element is defined as optional in the schema of  FIG. 1(   a ) and is required in the schema of  FIG. 1(   b ). This difference is the result of “minOccurs” being set to zero in the schema of  FIG. 1  ( a ). Unfortunately, if a company had its records stored in accordance with the schema of  FIG. 1(   a ) and wanted to recast the records into the schema of  FIG. 1(   b ), the records in accordance with the schema of  FIG. 1(   a ) that lack a “billTo” element would be invalid when cast into the schema of  FIG. 1(   b ). Thus, the element type “purchaseOrder” as set forth in the schema of  FIG. 1(   a ) is only sometimes valid when cast into the schema of  FIG. 1(   a ). Since the company may have millions of these records, the company would want to identify which records could be recast into the new schema, and which ones could not be recast, as quickly and as efficiently as possible. 
     A preferred method of determining whether or not a document that is structured in accordance with a first schema can be recast into a second schema is set forth in  FIG. 2 . The method begins in step  20  with identifying all of the element types and element tags defined in the first (source) schema and their possible pairings. The method then proceeds to step  22  wherein it identifies all of the element types and element tags defined in the second (target) schema and their possible pairings. The method then identifies sets of subsumed (S), disjoint (D) and intersecting (I) type-pairs in step  24 . 
     In step  26 , the method identifies sets of subsumed (ST), disjoint (DT) and intersecting (IT) element tag-type-pairs. In step  28  the method examines ST, DT and IT. If all element tag-type pairs that can be applied to root elements of a document are in ST, then the document may be validated as conforming to the target schema as set forth in step  50 . Otherwise proceed to step  30 . In step  30 , the top-most element tag of the document is identified, as well as its type according to the source schema (T 1 ) and the target schema (T 2 ). The method then calls the procedure of step  32 . If TRUE is returned the document is validated according to the target schema in step  50  and if FALSE is returned the document is invalidated according to the target schema in step  52 . Step  32  is the entry point to a procedure that accepts the document and a portion (subtree) with tag E whose type as determined for the source schema is T 1  and according to the target schema it is T 2 . In step  36  the method checks whether E-T 1 -T 2  is disjoint. If so, there is no point in the procedure further checking this subtree further and FALSE is returned in step  34 . Otherwise, the method proceeds to step  36  where it checks whether E-T 1 -T 2  is subsumed. If the answer is YES, the procedure can immediately return TRUE in step  38 . Otherwise, the procedure proceeds to check whether E-T 1 -T 2  is intersecting. This should be the case, and if not, there must have been an error and the method&#39;s execution aborts with an error in step  44 . Otherwise the procedure proceeds to step  46 , wherein the children, say n of them, of the element under consideration are identified, as well as their element tags (Ri), and types according to the source schema (T 1   i ) and according to the target schema (T 2   i ), for i=1, . . . , n. The procedure then proceeds to step  48  wherein it then performs up to n calls, one per child. In step  54 , these calls return, if any returns FALSE, the procedure call returns FALSE in step  38 . If all return TRUE, the procedure call returns TRUE in step  34 . 
     The present inventors have discovered that by limiting the portions of the document that need to be reviewed to determine its validity as set forth in more detail above and below, the amount of processing time required to validate a document can be substantially reduced. In particular, the structure of the source schema and its relationship to the target schema can be used to reduce the amount of the document that must be reviewed to determine its validity with respect to the target schema. The amount of reduction in the portions of the document that must be reviewed and the corresponding amount of processing time required to validate the document depend upon a number of factors such as the relationship between the source and target schema and the number of documents that need to be validated. However, the time required to process a given document can easily be reduced by as much as 50% in certain situations. The inventors have set forth a detailed proof of the concepts behind the present invention and the benefits obtained through its use in their article entitled “Documents Revalidated: Casting XML Documents in a Different Light” a copy of which is contained in the prosecution history of the parent application and the disclosure of which is hereby explicitly incorporated into the present application by reference. 
     Referring now to  FIG. 3 , a preferred method of determining whether or not a document that is structured in accordance with a first string schema can be recast into a second string schema is set forth. Such schemas may be specified with various known formalisms, including but not limited to: regular expressions, grammars, finite state automata, or a combination thereof. The method begins in step  70  with identifying the schema types of the first (source) schema and then onwards to step  72  with identifying the second (target) schema. The method then proceeds to step  74  wherein analysis is performed to determine subsumption, disjointness or intersection of the schema pair type 1 -type 2 . In step  76 , if subsumption is detected, the document may be immediately validated according to the second schema as set forth in step  88 . Otherwise, the method proceeds to step  78 . In step  78 , in case disjointness is detected, the document may be immediately invalidated according to schema  2  which is done in step  82 . Otherwise, the method proceeds to step  80 . In step  80 , if intersection (the only remaining logical choice) is not detected, an error must have occurred and the method proceeds to step  90  wherein an error is communicated. Otherwise the method proceeds to step  84  in which an immediate decision automaton for type 1  and type 2  is constructed. An immediate decision automaton is similar to a standard finite automaton, except that while scanning its input such an automaton can accept, or reject, its input prior to scanning the whole input. The particular immediate decision automaton, based on type 1  and type 2 , has such immediate transitions that are partially based on the knowledge that the input under consideration conforms to type 1 . Details of the construction are in “Documents Revalidated: Casting XML Documents in a Different Light” to which a reference was previously made. The method then proceeds to step  86 . In step  86 , the string document is scanned. During the scanning, the automaton may accept (validate) or reject (invalidate) the string document prior to completing its scanning, thereby realizing a substantial efficiency gain. 
     The method set forth in  FIG. 3  reduces the time required to validate a string document. First, it may avoid scanning the document if the type-pair is disjoint or subsumed. Second, in the case of an intersecting pair, by only revalidating a prefix of the document, substantial savings may often be realized. 
     Referring now to  FIG. 4 , a preferred method of determining whether or not a document that is structured in accordance with a first DTD schema can be recast into a second DTD schema is set forth. The method commences in step  120  wherein all tags in both DTDs, DTD 1  defining the first, source, schema, and DTD 2  defining the second, target, schema are identified. In DTD based schemas, each element tag is associated with exactly one type, or content model. In step  124  the sets of subsumed (ST), disjoint (DT) and intersecting (IT) element tag-type-pairs are computed. This computation is based on comparing automata corresponding to content models. Step  126  examines if all element tag-type-pairs that can apply to root elements of a document are in ST. If so, the document may be validated immediately (at step  138 ). Otherwise, in step  128 , a decision is made based on whether given a tag, all document element occurrences that use this tag may be accessed directly, that is without scanning sequentially through the document. If this is not the case, the method proceeds to step  130 . In step  130 , the procedure  32  of  FIG. 2  is utilized. If the procedure call returns TRUE, then the document is validated (in step  138 ), else it is invalidated (in step  140 ). In the case where direct access to elements based on tags is provided, the method proceeds to step  132 . In step  132 , the method checks whether the document contains an element whose tag, E, is associated with type 1  in the source schema and type 2  in the target schema such that E-type 1 -type 2  is in DT. The existence of such an element occurrence in the document invalidates it. Such invalidation is declared in step  140 . Otherwise, the method proceeds to step  134 . In step  134 , the elements in the document such that their tags appear together with some types, type 1  and type 2 , in IT are accessed. Such elements identify “suspicious” (i.e., non-complying or invalidating) portions of the document. The method checks, in step  136 , whether for such “suspicious” elements their content in the document satisfies the content model associated with their tag in the target schema. If for any such element satisfaction is not determined, the document is invalidated according to the target schema (step  140 ). If for all such elements satisfaction is detected, the document is validated according to the target schema (step  138 ). We note that checking compliance with a content model is a simple process that is limited to the element being tested. In addition, this compliance testing may be done sequentially, in parallel, or in combination thereof. Further, in some storage modes of XML documents, such as DOM, this test need not affect all the data in the tested element, rather, only the “top level” parent-child relationships need be checked. At any rate, the method of Application 2 (for strings, that uses automata-based techniques) may be used to speed up this test. 
     Referring now to  FIG. 5 , a preferred method of validating a modified document with respect to a schema B wherein the document was previously, in its original form, validated with respect to a schema A and then modified, is shown. The method commences in step  220 , wherein tags and types according to the first, source, schema are identified. Such identification is then performed for the second, target, schema, in step  222 . In step  224  subsumed, disjoint and intersecting type-pairs are identified. Then, in step  226 , subsumed (ST), disjoint (DT) and intersecting (IT) element tag-type-pairs are identified. In step  228 , if all element tag-type pairs that can apply to root nodes are in ST, validation may be deduced, in step  260 . Otherwise the method proceeds to call the procedure in step  234  in step  232 , with the whole tree as the subtree to be considered by the procedure. If the procedure call returns TRUE, validation is deduced in step  260 , otherwise invalidation is deduced in step  270 . We now describe the procedure defined in step  234  which contains the explicit handling of modified subtrees of this currently described method. Given a subtree to consider, in step  236 , the procedure determines whether the subtree under consideration has been modified from its original state. If it has not been modified, the method of  FIG. 2  is applied in step  238  and a result is appropriately returned. Otherwise, the subtree is not in an original subtree state. Step  240  then checks whether the subtree is a deleted subtree. In this case, it may be ignored and hence TRUE is returned in step  242 . Otherwise, the procedure checks in step  244  whether this subtree is newly inserted. If so, then there is no ‘prior information’ to be utilized and the subtree is validated by itself in step  246  which returns TRUE if validation succeeds and FALSE otherwise, as the results of this procedure call. Otherwise, the subtree is a modified subtree and the procedure proceeds to step  248 . In step  248 , the actual present tags of children of the subtree root element are considered. These are either original tags, modified tags or newly inserted tags. As a sequence, they are tested for satisfying the content model requirement of the subtree root tag and its type in the target schema. They are also temporarily labeled with their expected types according to the target schema. If the actual content does not conform to the content model according to the target schema, the procedure returns FALSE in step  250 . Otherwise, the children tags are also associated with their types according to the source schema (only original non-deleted children are so labeled) and the procedure proceeds to step  252 . Step  252  considers the children, their tags, their types according to the source schema and according to the target schema. A recursive call is performed for each child with a new subtree root (namely the child element), the source type, if any, and the expected target type, if any. These calls may be done sequentially, in parallel, or in combination thereof. If any such call returns FALSE, no more calls are performed, and FALSE is returned (step  250 ) as the result of this procedure call. Otherwise, all calls returned TRUE, and TRUE is returned in step  254  as the procedure call result. 
     As is apparent from the description of Application 4 in  FIG. 5 , this method may realize substantial savings by quickly validating unmodified subtrees by essentially applying the method of Application 1 ( FIG. 2 ) to such subtrees, by ignoring deleted subtrees, by validating “stand-alone” newly inserted subtrees, and by efficiently handling modified tags by processing “in parallel” their children, thereby being able to utilize the knowledge of conformance to the source schema even as progressing “down the tree” over modified elements (this is the essence of step  252 ). A special case of this scenario would be when the modifications to the first schema result in the first schema being the same as the second schema. In such a case, it would only be necessary to validate the documents with respect to either the first schema or the second schema in order to establish the documents validity with respect to both schemas. 
     Referring now to  FIG. 6 , a preferred method of validating a modified document with respect to a string schema B wherein the document was previously, in its original form, validated with respect to a string schema A and then modified, is shown. The method commences in step  370 , wherein the type according to the first, source, schema is identified. Such identification is then performed for the second, target, string schema, in step  372 . The method proceeds to step  384 . In step  384 , three automata are constructed, Ma—an ordinary automaton for validating documents according to type 1 , Mb—an immediate decision automaton for validating documents according to type 2 , and Mc—an immediate decision automaton for validating documents that are valid according to both type 1  and type 2 , which is built out of Ma and Mb (its set of states is the cross product of the set of states of Ma and the set of states of Mb). The method proceeds to step  386 . In step  386 , Mb is evaluated against the document, up to and including the rightmost position beyond which the document is identical to what it was originally, call this position i. During this evaluation, Mb may accept, in which case the document is validated according to type 2  in step  388 . Otherwise, Mb terminates the evaluation in a set of states Qb. The method proceeds to step  390 . Evaluate Ma on the original document up to position m such that the original string past position m is identical to the modified document past position i. Let Qa be the resulting set of states. The method proceeds to step  392 . At this point, Qa and Qb are used to initialize the starting set of states, Qa X Qb (we use X to denote the cross product), of Mc, which is operated to evaluate the document past position i. If Qc accepts, possibly immediately during evaluation, then the document is validated in step  388 . Otherwise, the document is invalidated in step  382 . 
     As is apparent from the description of Application 5 in  FIG. 6 , this method may realize substantial savings by applying the automaton Mb to the modified portion and the automaton Mc to the unmodified (identical to original) suffix of the document. The method of Application 5 can be used in verifying content models within Application 4, thereby improving Application 4. 
     Referring now to  FIG. 7 , a preferred method of validating a modified document with respect to a DTD schema B wherein the document was previously, in its original form, validated with respect to a DTD schema A and then modified, is shown. The method commences in step  720  with identifying tags and types in the first, source, schema; then proceeds to step  722  and identifies tags and types in the second, target, schema. The method then proceeds to step  724  wherein tags (that completely determine the element tag-type-pair combination) are classified as subsumed, disjoint or intersecting. If, in step  726 , direct access to element tags is not provided, the method calls, in step  730 , the Procedure at step  234  of Application 4 ( FIG. 5 ). Based on the call, the document is either validated (TRUE is returned) or invalidated (FALSE is returned). Otherwise, direct access is provided, for example by using a tree data structure, and the method proceeds to step  728 . In step  728 , the method checks whether there are any unmodified document elements whose tags appear in DT (i.e., cannot possibly be valid according to their content model in the target schema). If such elements exist, the method invalidates the document in step  740 , otherwise it proceeds to step  732 . In step  732 , newly inserted elements are treated (in parallel, or sequentially). For each such element, if its children tags do not satisfy its content model (i.e., of type 2 ) according to the target schema, the document is invalidated (in step  740 ). Otherwise, the method proceeds to step  734  wherein the method treats all modified elements, whose tags are as they were originally, but their immediate children tags have been modified. (Access to such elements is provided by accessing new elements or elements whose tags were modified and proceeding to their parents). The method checks whether it is the case that for each such element, with say tag E, its children tags satisfy the content model of E in type 2 . If it is the case, the method proceeds to step  736 , otherwise the method invalidates the document in step  740 . In step  736 , the method treats all modified elements, whose tags have been modified. Consider an element previously having tag E 1  and now having tag E 2 . The method checks whether it is the case that for each such element, its children&#39;s tags satisfy the content model of E 2  in type 2 . In case they do, the method proceeds to step  742  and otherwise invalidates the document according to the target schema in step  740 . In step  742 , the method treats all unmodified elements, whose tags appear in IT. The method checks whether it is the case that for each such element, with say tag E, its children&#39;s tags satisfy the content model of E in type 2 . If it is the case that not all unmodified elements are such, the document is invalidated in step  740 . Otherwise, it is validated in step  738 . 
     It is apparent that the method of Application 6 ( FIG. 7 ) can realize substantial efficiency over ordinary methods of revalidation. As is apparent, only relevant portions of the document are examined. In performing step  734 , the method of Application 5 can beneficially be used. In performing step  742 , the method of Application 2 can beneficially be used. In performing step  736 , the method of Application 2 may be used (if children tags are unchanged) or the method of Application 5 may be used (if children tags were changed). The usage of the methods of Applications 2 and 5 can further enhance performance of this method (Application 6). 
     Referring now to  FIG. 8 , a block diagram of an information handling system constructed in accordance with an embodiment of the present invention is shown. The information handling system is for retrieving documents that have been validated in conformance with a source schema from a source database  150 , validating the documents in accordance with a target schema and storing the documents in a target database  152 . A processor  154  controls the information handling system. While the information handling system is described as a single entity with regard to  FIG. 8 , it will readily be appreciated by those skilled in the art that the functions performed by the invention could be spread across the World Wide Web or a more localized network. For example, the source database  150  and target database  152  could be stored in a local memory or on a storage device such as a compact disc and accessed via a CD ROM  158 . Alternatively, the source database  150  and target database  152  could be stored remotely and accessed via an internet connection  156  or dial up connection (not shown). Thus, although, the nature of modern computing allows the various functions of the invention to be implemented separately at different remote locations under the control of the processor  154 , the functions and equipment for implementing the invention are unchanged. 
     The processor  154  first creates the first source schema description  164 , which is stored in an application memory  160 , from a schema in the source database  150 . The source schema description  164  identifies the various types of information or elements present in any document that conforms to the source schema description and the general layout or structure of such a document. A document type definition or standardized XML schema could be used by the processor  154  to create the source schema description  164 . The processor  154  then creates a target schema description  162  which is also saved in the application memory  160  from a schema from the target database  152 . In a fashion similar to the source schema description  164 , the target schema description  162  specifies the expected type and structure of the data contained in a document that conforms to the target schema. Alternatively, the target schema description  162 , like the source schema description  164 , may be independently created and retrieved by the processor  154  from a remote source. 
     Once the source schema description  164  and target schema description  162  have been retrieved by the processor  154 , they are preprocessed by the processor to also create a subsumed description  170 . The subsumed description  170  identifies element tag-type-pairs, of the form tag-type 1 -type 2 , such that if a document element with the tag is determined to have type 1  with respect to the source schema then it conforms to type 2  according to the target schema. For example, if an element type in the target schema covers every possible element of a source schema element type, the target element type subsumes the source element type. In such a case, all elements in a source document of the subsumed element type are necessarily valid in the target schema according to the subsuming type. Therefore, the subsumed description  170  is used to identify element types in the document that conform to the source schema that are immediately identifiable as valid in the target schema. A disjointed description  168  is also created by the processor  154  and stored in the application memory  160 . The disjointed description  168  is used to identify immediately invalidating conditions in the documents valid with respect to the source schema that immediately result in the document being declared invalid with respect to the target schema. More particularly, the disjointed description  168  identifies element tag-type-pairs, of the form tag-type 1 -type 2 , such that when an element with the tag is determined to have type 1  according to the source schema then it cannot be validated as having type 2  with respect to the target schema. If any of these elements with such a tag and type according to such type 1  are present in a document in the source database  150 , the document can not be cast into the target schema without being modified. Finally, the source definition schema  164  and the target definition schema  162  are processed to generate an intersection description  166 . As discussed above, the intersection description  166  identifies element tag-type-pairs, of the form tag-type 1 -type 2  such that an element with the tag of type 1  which is valid with respect to the source schema is sometimes valid according to type 2  in the target schema. The intersection description is created by comparing the element definitions in the source schema to those in the target schema and making decisions about whether document elements valid according to an element type defined in the source schema can be valid with regard to an element type defined in the target schema. Thus, depending upon the particular layouts of the source schema and the target schema, the intersection description  166  may or may not exist. The above exposition was in terms of element tag-type-pairs. The above descriptions (disjoint, subsume, intersecting) also contain such information with respect to types alone (in addition to such information in conjunction with tags). The reader versed in the art realizes that the source and target schema specifications may be in terms of XML Schema or similar language (e.g., for specifying web services formats), in terms of DTDs or in terms of string schemas. Further, the description may also be in terms of a schema language for databases (such as ERD, SQL, OMG) or for an object layout specification (as in Java, C# and C++). The techniques of this invention are suitable for casting also between different formalisms, for example from XML document to Java objects. Those versed in the art may also appreciate that documents may be stored in various formats in the databases  150  and  152 . Such formats include but are not limited to: raw text, compressed text, DOM, serialized DOM, serialized programming objects, and streams. 
     An exemplary use of the information handling system shown in  FIG. 8  is set forth below. The process begins with the processor  154  receiving a request to cast a series of documents stored in a source database  150  in accordance with a source schema into a target schema. The request could be received from the internet connection  156  or a user input/output terminal  172 . The request preferably identifies a set of documents to be validated, a target schema in which to validate the documents and a location in which to store the recast documents. Once the processor  154  has received the request, the processor  154  creates the descriptions  162 ,  164 ,  166 ,  168  and  170  as set forth above. The processor  154  then retrieves the first document to be validated from the source database  150  and examines the document with the disjointed description  168 . If the disjointed description  168  and the intersection description  166  are both empty, the document is immediately validated as it contains only subsumed element-type-pairs, and the processor  154  retrieves the next document from the source database  150 . Otherwise, the processor  154  examines the document, starting at the topmost element. The examination is a recursive process that is now explained with respect to any element with an element tag, tag, and type, type 1 , with respect to the source schema whose determined type should be type 2  with respect to the target schema. For such an element, the following cases are considered: 
     tag-type 1 -type 2  is in the disjoint description  168 . In this case invalidation according to the target schema is immediate. The recursive call returns to its origin indicating success (FALSE). 
     tag-type 1 -type 2  is in the subsumed description  170 . In this case validation of the element is immediate with respect to the target schema. The recursive call returns to its origin indicating success (TRUE). 
     tag-type 1 -type 2  is in the intersection description  166 . In this case, we need to continue checking “down the tree”. The children elements are considered. First it is verified that the concatenation of their tags is in the content model of type 2 . Then, each child element is validated, recursively, based on its assigned type according to the target schema. If all such recursive validations return TRUE, overall TRUE is returned out of this recursive call. 
     The present disclosure includes the portions that are contained in the appended claims, as well as that of the foregoing description. Although this invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and scope of the invention.