Schema Binding Proposal

Transcription

1 SchemaBindingPrpsalV2WG ChangeBars.dc Schema Binding Prpsal Sandy Ga Valentina Ppescu 1 Terminlgy Schema dcument: Schema: an <xs:schema> element; can be an XML fragment a set f schema cmpnents; a schema is nrmally (but nt required t be) cnstructed frm ne r mre schema dcuments Schema cmpnent: an element declaratin r a type definitin r a particle r Include: Redefine: Imprt: A schema dcument can include anther schema dcument using <xs:include>. Bth schema dcuments cntribute t the same schema; and bth crrespnd t schema cmpnents frm the same target namespace (r n namespace). If the included schema dcument des nt have a target namespace, namespace f the including schema dcument is used. Similar t include, but use <xs:redefine>, and the redefining schema dcument can replace certain included cmpnents with new cmpnents. Allws the imprting schema dcument t refer t cmpnents frm the imprted namespace (r n namespace), which must be different frm the imprting schema dcument s target namespace. If the cmbinatin f the namespace attribute and the schemalcatin attribute n <xs:imprt> reslves t a schema dcument, then the resulting schema als includes cmpnents frm the imprted schema dcument. Schema cmpsitin: (In this dcument) cnstruct a single schema frm multiple schema dcuments, using the abve include, redefine and/r imprt mechanisms. Nte: a schema is nt equal t a schema dcument! 2 Prblem definitin In perfrming SML mdel validatin ver the SML mdel packaged in an SML-IF instance, assciatins between XML Schema definitin dcuments and instance dcuments need t be drawn, bth t cmpletely validate XML Schema dcuments themselves (t make sure they prduce valid schemas) and t establish schema-validity f the instance dcuments. validating Schema dcuments can be cnnected with ther schema dcuments using cmpsitin features prvided by XML Schema. This includes <xs:include>, <xs:redefine>, and <xs:imprt>. A schema dcument s validity may depend n ther schema dcuments it includes/redefines/imprts, r even ther schema dcuments that include/redefine/imprt it. When validating a mdel instance dcument, a precise list f schema dcuments need t be assciated with it fr a schema and the instance dcument is schema-assessed using this schema. an The XML Schema 1.0 specificatin prvides mre flexibility in cnstructing the schema used fr assessment than is apprpriate fr the semantics defined by SML and SML-IF validatin: It allws prcessr latitude in terms f lcating schema dcuments (reslving namespace and schema lcatin attributes) and cmpsing schema dcuments tgether t frm a single schema.

2 SchemaBindingPrpsalV2WG ChangeBars.dc Schema lcatin attributes can be ignred in sme cases ( xsi:schemalcatin in instance dcuments and schemalcatin n <xs:imprt>); and allwed t fail t reslve in thers ( schemalcatin attribute n <xs:include> and <imprt>). Knwn schema and SML implementatins behave differently with respect t hw/whether they prcess schema lcatin attributes. Multiple imprts f the same namespace allw all but the first ne t be ignred. S it is clear that we have n hpe f guaranteeing general case interperability using anything based nly n XML Schema given the cnstraints abve, and SML-IF needs t specify hw t determine such assciatins. NOTE: this prpsal is nly abut SML mdel validatin, and nt SML-IF validatin (against the IF schema). Unless therwise indicated, validatin/validity in the fllwing sectins is always abut SML mdel validatin. 3 Requirements 3.1 Supprt schema cmpsitin There are many real-life schemas that are cnstructed frm multiple schema dcuments. Such schemas may span multiple namespaces (hence the need fr imprt); cmpnents frm each namespace may be further divided int multiple schema dcuments (hence the need fr include). Schema has a feature ften referred t as chamelen include. This means that a schema dcument with a target namespace includes r redefines anther schema dcument withut a target namespace, and the result is as if the included/redefined dcument had a target namespace that s the same as the including/redefining dcument. SML-IF needs t supprt this usage scenari. 3.2 Supprt schema versining Schema authrs can t anticipate hw their schemas will be used, hence the need t evlve schemas. There are different versining scenaris. There are cases where minr mdificatins f lder versins suffice, and redefine can be used. Sme schemas need t be rewritten t accmmdate new requirements, and new namespace may r may nt be intrduced (cmpatibility is ften a gd reasn fr nt changing namespaces). There are als cases where there are generic and specific versins (as ppsed t previus and next versins), which ften c-exist and share the same namespace. T supprt this, SML-IF needs t be able t package in the same SML-IF instance different versins f the same schema in the same namespace. 3.3 Deterministic Fr a given SML-IF instance, there MUST be n ambiguity in determining hw schema dcuments (that are included in this instance) are cnnected using <xs:include>, <xs:redefine>, and <xs:imprt>, and therefre MUST be n ambiguity in determining which schema dcuments are used t frm a schema against which a given instance dcument is validated. 3.4 Full schema supprt Being a generic validatin language, SML supprts all schema features. Being a mechanism t transmit SML mdels, SML-IF als needs t supprt full schema features, especially <xs:include>, <xs:redefine>, and <xs:imprt>. Fr example, in an SML mdel, if an instance dcument I is validated against a schema frmed frm a schema dcument A, which redefines schema dcument B, then it MUST be pssible t transmit I, A, and B in an SML-IF instance and maintain their relatinship.

3 SchemaBindingPrpsalV2WG ChangeBars.dc 3.5 Schema dcument exchange An SML-IF dcument can cntain XML Schema dcuments within its definitin dcuments that are attached fr exchange purpses nly. These dcuments are nt intended t be used fr XML Schema validity assessment f the mdel instance dcuments. SML-IF needs t supprt this use case and ensure that dcuments f this purpse d nt participate in mdel instance dcument validatin. This is analgus t the case we already have fr rule dcuments, except rule dcuments d nt have a bind t all default as we are cntemplating fr XML Schema dcuments. Any new types f definitin dcuments added in the future will have t address similar cncerns, whse syntax will be influenced by the default binding (all r nne). Definitin dcuments purpse have n relatinship with the attached instances and they validatin purpses within the SMLIF dcument. Nte that fr bth schema dcuments and Schematrn rule dcuments that are nt bund t any instances, their validity shuld still be checked when assessing SML mdel validity, as required by SML, which has: Each XML Schema dcument in the mdel's definitin dcuments MUST satisfy the cnditins expressed in Errrs in Schema Cnstructin and Structure ( 5.1). [XML Schema Structures] Each Schematrn dcument in the mdel's definitin dcuments MUST be a valid Schematrn dcument [ISO/IEC ] 4 Cnstraints 4.1 Supprt access t schema dcuments utside f SML-IF We d nt want t frce all schemas necessary t validate the mdel instance dcuments packaged by a single SML-IF instance t be included by value in every SML-IF instance. It is nt clear this wuld even be sensible in a repsitry interchange scenari, let alne the mre general case f usage scenaris sme have mentined fr SML-IF like web services message exchanges. 4.2 Ignrable schema lcatins We cannt require hnring f xsi:schemalcatin and xsi:nnamespaceschemalcatin in instance dcuments r schemalcatin n <xs:imprt>, because Sme existing implementatins ignre them Hnring schema lcatin in instance dcuments may have security cnsequences Schema specificatin des require that prcessrs attempt t reslve schema lcatins specified n <xs:include> and <xs:redefine>. It is nt an errr fr such attempt t fail fr <xs:include>. It is an errr when <xs:redefine> cntains nn-anntatin cntent. It s mre flexible fr <xs:imprt>. Schema allws any strategy fr prcessrs t lcate cmpnents t imprt, based n either r bth f the namespace and the schema lcatin. 4.3 Include definitin and instance dcuments as-is SML-IF instance prducers may nt have cntrl ver the cntent f the schemas necessary fr validatin f mdel instance dcuments, where cntrl means what is cded in the files. I.e. there will be cases where xs:imprt and xs:include are cded, with and withut schemalcatin, and multiple files cntaining schema cmpnents fr the same namespace will be bserved.

4 SchemaBindingPrpsalV2WG ChangeBars.dc 4.4 Lazy schema assembly Schema specificatin allws schemas t be assembled lazily. A partial schema can be used t validate an instance dcument, and mre cmpnents can be added t the schema during the validatin, as lng as the new cmpnents dn t change the validatin result f infrmatin items that are already validated. This is smetimes nt easy t enfrce, but a cnsequence f supprting full schema implies that SML-IF validatin cannt vilate this cnstraint. 4.5 Supprt reference cnstraints Reference-related cnstraints (targetelement, targettype, acyclic, SML identity cnstraints) need t be prperly supprted. When 2 dcuments A and B are cnnected by an SML reference, these cnstraints require the ability t determine whether a cmpnent frm the schema used t assess A is identical t a cmpnent frm the schema used t assess B. The schema spec desn't define identity f cmpnents acrss multiple schemas. The same surce declaratin may prduce ttally different cmpnents in different schemas. S t check thse reference-related cnstraints, related instance dcuments MUST be validated using the same schema. 5 Interperability Apprach We divide the universe f SML-IF dcuments int tw disjint subsets: A set that have all schema dcuments included, by value (smlif:data) and/r by reference (smlif:lcatr), in the SML-IF instance; the schema-cmplete set All ther SML-IF dcuments; the schema-incmplete set It is necessary fr a prducer t declaratively distinguish between these tw cases, since it is nt always pssible t distinguish based n the cntent alne. Fr example, XML Schema allws xs:include s schema lcatin attribute s value t nt reslve, althugh the value is required. This can be dne by intrducing a schemacmplete attribute n the <smlif:definitins> element t indicate whether this SML- IF instance includes all necessary definitin dcuments. When this attribute is specified with an actual value true, then fr the instance t be valid, its schema definitin dcuments and instance dcuments can nly refer t either built-in cmpnents r cmpnents frm definitin dcuments included in the instance. Built-in cmpnents include: 4 xsi: attributes (defined by XML Schema) all schema built-in types (xs:anytype and simple types defined in XML Schema Part 2) sml:ref attribute declaratin sml:uri element declaratin Remember, this is nt trying t say that SML-IF dcument instances in the schema-incmplete set are nw invalid. It des say that SML-IF cannt guarantee interperability fr the schema-incmplete set. 6 Schema binding prpsal 6.1 An Example (See the picture next page) Assume an SML mdel packaged in an IF dcument has 4 schema dcuments: xsd1-a and xsd1-b have target namespace ns1, and xsd2-v1 and xsd2-v2 have target namespace ns2, where xsd2-v1 and xsd2-v2 are cnflicting versins f the same schema (same target namespace). There are 4 instances: dc1 uses xsd1-a and xsd1-b; dc2-v1-a and dc2-v1-b uses xsd2-v1, and dc2-v2 uses xsd2-v2. All dc2-* instances have SML references t dc1, and their references have targettype cnstraints, pinting t a cmpnent in ns1. Mre precisely, if during validatin f schema r instance dcument in the IF instance, n attempt is made t retrieve schema dcuments utside f the set f schema dcuments included in the IF instance, r t retrieve schema cmpnents utside f the set f cmpnents cnstructed frm schema dcuments included in the IF instance, then the IF instance is said t be within the cmplete set. The nly exceptin t the abve rule is fr the built-in cmpnents. These cmpnents are always available in SML-IF prcessrs. They can be referred t freely, withut the need t explicitly lad them. <#>des sml:reftype belng here (depends n hw we reslve bug 4673)? There are several ways t specify hw t lcate schema dcuments that are used t cnstruct a schema. Each apprach needs t answer the fllwing questins: <#>Hw t handle <xs:include> <#>Hw t handle <xs:redefine> <#>Hw t handle <xs:imprt> <#>Hw t lcate the crrect versin f each schema dcument used t validate a given instance In XML Schema, schema cmpsitin is achieved using ne r mre f <xs:include>, <xs:redefine>, and <xs:imprt>. Schema desn t prvide details abut hw t assemble a schema frm unrelated schema dcuments. T achieve interperability, the fllwing subsectins always describe varius appraches as having a synthetic rt schema dcument whse transitive clsure ver include/redefine/imprt cvers all schema dcuments that are suppsed t be used. This is similar t hw XSLT 2.0 determines hw schemas shuld be assembled. Implementatins are nt required t implement schema assembly using synthetic schema dcuments. <#>Namespace matching In the SML-IF instance, there is a namespace t schema dcument mapping. Such a mapping can be established by, fr example, traversing all schema dcuments and gathering their target namespace attributes. If fr a given namespace, there is mre than ne schema dcument, then a chice must be made abut which t use. This text assumes that all dcuments fr the namespace are lgically merged, as if the cnsumer synthesized anther schema dcument with this namespace as its target namespace and includes all these dcuments. This synthetic

5 SchemaBindingPrpsalV2WG ChangeBars.dc T check targettype, dc2-v1-a, dc2-v1-b and dc1 must be validated using the same schema (xsd1- a + xsd1-b + xsd2-v1); similarly, dc2-v2 and dc1 must be validated using the schema frm xsd1-a + xsd1-b + xsd2-v2. Mre cncretely, in the fllwing picture, instances in the red rectangle are validated using the schema built frm schema dcuments in the red val; and instances in the blue rectangle are validated using the schema built frm the blue val. Nte that dc1 is validated twice using 2 different schemas. dc1 may als be validated against nly xsd1; this is up t the mdel authr t specify. xsd2-v1 dc2-v1-a dc2-v1-b xsd1-a xsd1-b dc1 xsd2-v2 dc2-v2 6.2 Slutin t the Example <schemabindings> <!-- Each "schemabinding" element crrespnds t a schema and mdel instance dcuments that are assessed against this schema --> <schemabinding> <!-- all "namespacebinding" children tgether build the schema --> <namespacebinding namespace="ns1" aliases="xsd1-a xsd1-b"/> <namespacebinding namespace="ns2" aliases="xsd2-v1"/> <!-- list all applicable instances; same as fr rule bindings --> <dcumentalias>dc1</dcumentalias> <dcumentalias>dc2-v1-a</dcumentalias> <dcumentalias>dc2-v1-b</dcumentalias> </schemabinding> <schemabinding> <namespacebinding namespace="ns1" aliases="xsd1-a xsd1-b"/> <namespacebinding namespace="ns2" aliases="xsd2-v2"/> <dcumentalias>dc1</dcumentalias> <dcumentalias>dc2-v2</dcumentalias> </schemabinding> </schemabindings> <definitins schemacmplete="true"> <!-- schema dcuments fr xsd1-a, xsd1-b, xsd2-v1, xsd2-v2 --> </definitins> <#>Explicit schema binding With this apprach, the SMLIF prducer prvides an explicit mapping f namespace t schema dcument alias(s). The fllwing bindings shuld be supprted: <#>6.2.1 Glbal schema binding The mapping fr each namespace t a set f schema dcuments can be defined at the SML-IF instance level by specifying explicit mappings fr namespaces, t verride the default namespace match all apprach described in sectin 6.1. This explicit binding f a namespace with a set f schema dcuments can be used t fulfill requirement 3.5. Fr the situatin when a definitin dcument is attached t the SMLIF with the intentin f just exchanging the data, an explicit binding f its targetnamespace with the crrect schema dcument(s) can slve the match-all namespace matching apprach issue identified in sectin 7, since the glbal binding will verride the match-all namespace matching apprach. <#>6.2.2 Definitin-level schema binding Each schema dcument can prvide its wn namespace t schema dcument alias mapping, which verrides any glbal level binding fr these namespaces. That is, fr a given namespace, if it s specified in the definitin-level binding then use it; therwise if it s specified in the glbal binding then use this ne; therwise use the default namespace t schema dcument mapping as defined in sectin 6.1

6 SchemaBindingPrpsalV2WG ChangeBars.dc 6.3 Frmal Prpsal 1. Change the IF dcument structure t add the fllwing (new cntent highlighted): <mdel>... <rulebindings>? <rulebinding> * <dcumentalias="xs:anyuri"/>? <rulealias="xs:anyuri"/> </rulebinding> </rulebindings> <schemabindings>? <schemabinding> * <namespacebinding/> * <!-- a single namespace name and and list f schema dcument aliases --> <dcumentalias/> * <!-- a list f instance dcument aliases --> </schemabinding> </schemabindings>... <definitins schemacmplete= xs:blean >?... </mdel> The details f the preceding XML syntax, e.g. whether the data is cntained in attributes r elements, is fully negtiable. The XML abve simply captures enugh t have the discussin that fllws. 2. Fr every schema binding SB in the mdel, i.e. every /mdel/schemabindings/schemabinding element (using XPATH ntatin): 2.1. Cmpse a schema using all dcuments specified under all SB s <namespacebinding> children 2.2. Whenever there is an <imprt> fr a namespace N If there is a <namespacebinding> child f SB whse "namespace" matches N, then cmpnents frm schema dcuments listed in the crrespnding "aliases" are used. As with rule bindings, URI prefixing is used fr matching schema dcument aliases. Nte: at mst ne <namespacebinding> is allwed per namespace N within a given SB. If mre than ne namespace binding exists fr the namespace as part f a single schema binding, the SML-IF instance is in errr. Nte: if the set f aliases fr namespace N is empty, the namespace has n schema dcuments defining it in the schema binding Otherwise if there are schema dcuments in the IF whse targetnamespace is N, then cmpnents frm all thse schema dcuments are used Otherwise If a schema-cmplete dcument (/mdel/definitins/@schemacmplete=true) is being prcessed, then n cmpnent frm N (ther than built-ins) is included in the schema being cmpsed Otherwise, it is implementatin-defined whether the prcessr tries t retrieve cmpnents fr N frm utside the SML-IF instance 2.3. Whenever there is an <include> r <redefine>, the schemalcatin is used t match aliases f schema dcuments, as with base SML-IF If there is a schema dcument in the IF matching that alias, then that dcument is used Glbal schema binding wrks nly when a namespace is always defined by the same definitin dcument(s), fr all schema instances. Fr the case when tw instances refer t the same namespace but the namespace is defined by tw different definitin dcuments, an instancelevel binding will be applied (instance A refers t namespace ns, defined in definitin dcument A1; instance B refers t the same namespace ns defined in definitin dcument B1.) <#>6.2.3 Instance-level schema binding Each instance dcument can prvide its wn namespace t schema dcument alias mapping, which will verride any glbal r definitin-level bindings fr these namespaces.. That is, fr a given namespace, if it s specified in the instance-level explicit binding, then use it; therwise if it s specified in a definitin-level binding at the schema dcument level (fr sme schema dcuments that s already used by this instance), then use it; therwise if it s specified as a glbal schema binding, then use it; therwise use the default namespace t schema dcument alias mapping. If the listed schema dcuments include r redefine ther schema dcuments, then they are reslved using aliases; all imprts are ignred, because the explicit list shuld have included all f them. <#>6.2.4 Reusable dcument -level binding If there are many dcuments in the same SML-IF that share the same/similar list f schema dcuments, then repeating that fr each dcument will becme a perfrmance burden. We can imprve efficiency f dcument-level binding by making it pssible t name the bindings s that they can be used by mre than ne dcument. <#>Brute Frce schema binding Use instance-level schema binding as the nly surce t lcate schema dcuments fr a given namespace. That is, every instance dcument in the IF dcument MUST specify namespaces used by that dcument and schema dcuments used fr that namespace. Reusable instance-level binding can als be used with this apprach. <#>7. Analysis <#>7.1 Namespace matching Namespace matching is easier t specify, understand, and implement. But it desn t have prper supprt fr: <#>Chamelen include/redefine. The included/redefined dcument wuld

7 SchemaBindingPrpsalV2WG ChangeBars.dc Otherwise If it's a schema-cmplete set, then the <include> r <redefine> is unreslved (which is allwed by XML Schema validity assessment rules) Otherwise, it's implementatin-defined whether it tries t reslve <include> r <redefine> t schema dcuments utside the IF 2.4. The list f <dcumentalias> dcuments are assessed against this *same* schema. targetxxx and identity cnstraints can nw be checked. Similar t <dcumentalias> under <rulebinding> elements, each <dcumentalias> can refer t multiple dcuments via URI prefixing. 3. Cmpse a schema using *all* schema dcuments included in the IF, then use this schema t assess thse instance dcuments that are nt included in any <schemabinding>. Nte: in the cmmn case where match-all namespace matching is the desired result, this is achieved by mitting <schemabindings>, i.e. withut intrducing any additinal cmplexity int the SML-IF instance. Nte: ne implicatin f this frmulatin is that the Schema dcument exchange requirement f sectin 3.5 is supprted. This wuld be dne by explicitly binding /mdel/instances/* t a schema binding that excludes the exchange-nly schemas. The mdel instance dcuments may still cntain infrmatin items frm namespace(s) in the exchange-nly schemas, hwever thse schema dcuments wuld nt be used t assess schema validity f the mdel instance dcuments. 6.4 Prpsal Analysis Great synergy with <rulebindings> It wrks in a way very similar t Schematrn rules. Yu assciate a schema (built frm a set f schema dcuments) with a set f instance dcuments Handles all the requirements Supprts schema cmpsitin: chamelen included dcuments is supprted by remving them frm the crrespnding <namespacebinding> (whse namespace attribute is absent) Supprts schema versining: multiple versins can be specified in different <schemabinding> elements Deterministic: the assciatin between instances and schemas is deterministic Full schema supprt: <include/redefine/imprt> are all supprted Schema dcument exchange: similar t chamelen included dcuments, exchange-nly dcuments can als be mitted frm the crrespnding <namespacebinding> Meets all the cnstraints Supprts access t schema dcuments utside f SML-IF: when schemacmplete=false, prcessrs are allwed t use external schema dcuments Ignrable schema lcatins: all xsi:schemalcatin attributes can be ignred Includes definitin and instance dcuments as-is: n need t mdify any included dcument; dcument aliases are used. Lazy schema assembly: the schema is knwn up-frnt; n need t handle lazy assembly Supprts reference cnstraints: instances specified under the same <schemabinding> use the same schema, s reference cnstraints can be checked. Simple t understand This has may Nte that the trivial case is als handled by bullet 2. That is, there is n <schemabinding> and all instance dcuments are assessed against the same schema.

8 SchemaBindingPrpsalV2WG ChangeBars.dc 7 Implementatin Cst We have t assume that all existing schema prcessrs are capable f handling the "namespace matching" apprach. That is, they can cmpse a schema frm a list f schema dcuments. This apprach shuld be straightfrward t handle. All the SML prcessr needs t d is t cmpute a list f schema dcuments based n schema dcuments mentined in <schemabinding> and give that list t the schema prcessr. The Explicit Binding apprach frm earlier iteratins f this prpsal had what we believe is equivalent functin, but was eliminated because it als had greater cmplexity (fur levels f binding t sift thrugh, instead f the tw used here, i.e. schema binding and match-all namespace matching). 8 Acknwledgement Jhn Arwe, Bassam Tabarra, Harm Sluiman, and Pratul Dublish all prvided useful input int the frmulatin f this dcument. This des nt imply their endrsement f the prpsal.

9 There are several ways t specify hw t lcate schema dcuments that are used t cnstruct a schema. Each apprach needs t answer the fllwing questins: Hw t handle <xs:include> Hw t handle <xs:redefine> Hw t handle <xs:imprt> Hw t lcate the crrect versin f each schema dcument used t validate a given instance In XML Schema, schema cmpsitin is achieved using ne r mre f <xs:include>, <xs:redefine>, and <xs:imprt>. Schema desn t prvide details abut hw t assemble a schema frm unrelated schema dcuments. T achieve interperability, the fllwing subsectins always describe varius appraches as having a synthetic rt schema dcument whse transitive clsure ver include/redefine/imprt cvers all schema dcuments that are suppsed t be used. This is similar t hw XSLT 2.0 determines hw schemas shuld be assembled. Implementatins are nt required t implement schema assembly using synthetic schema dcuments. Namespace matching In the SML-IF instance, there is a namespace t schema dcument mapping. Such a mapping can be established by, fr example, traversing all schema dcuments and gathering their target namespace attributes. If fr a given namespace, there is mre than ne schema dcument, then a chice must be made abut which t use. This text assumes that all dcuments fr the namespace are lgically merged, as if the cnsumer synthesized anther schema dcument with this namespace as its target namespace and includes all these dcuments. This synthetic schema dcument is used in the abve namespace t schema dcument mapping. Fr each mdel instance dcument, cnstruct a list f namespace names that are used by this instance (e.g. namespace f elements, attributes, r xsi:type values). Synthesize a schema dcument that imprts all these namespaces, with schema lcatins pinting t schema dcuments frm the namespace t schema dcument mapping. The schema crrespnding t this synthetic schema dcument is used t validate the instance. <xs:include> and <xs:redefine> are handled by matching the schemalcatin value with aliases f schema dcuments. <xs:imprt> is handled by ignring its schemalcatin value and always using the dcument frm the namespace t schema dcument mapping. Selective namespace matching The abve describes the all match alternative f the namespace matching apprach. There are ther pssibilities. Fr example first match means that fr each namespace, the first dcument with that namespace as its target namespace is used in the mapping. <xs:include> and/r <xs:redefine> are used if ther dcuments frm the same namespace need t be taken int accunt.