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Created: May 03, 2001.
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W3C XML Schema Published as a W3C Recommendation.

The World Wide Web Consortium (W3C) has announced the publication of the W3C XML Schema specification as a W3C Recommendation. A W3C 'Recommendation' "indicates that a specification is stable, contributes to Web interoperability, and has been reviewed by the W3C Membership, who are in favor of supporting its adoption by academic, industry, and research communities. XML Schemas define shared markup vocabularies, the structure of XML documents which use those vocabularies, and provide hooks to associate semantics with them. With over two years of development and testing through implementation, XML Schema provides an essential piece for XML to reach its full potential. The XML Schema specification consists of three parts. One part defines a set of simple datatypes, which can be associated with XML element types and attributes; this allows XML software to do a better job of managing dates, numbers, and other special forms of information. The second part of the specification proposes methods for describing the structure and constraining the contents of XML documents, and defines the rules governing schema-validation of documents. The third part is a primer, which explains what schemas are, how they differ from DTDs, and how someone builds a schema. XML Schema introduces new levels of flexibility that may accelerate the adoption of XML for significant industrial use. For example, a schema author can build a schema that borrows from a previous schema, but overrides it where new unique features are needed. XML Schema allows the author to determine which parts of a document may be validated, or identify parts of a document where a schema may apply. XML Schema also provides a way for users of ecommerce systems to choose which XML Schema they use to validate elements in a given namespace, thus providing better assurance in ecommerce transactions and greater security against unauthorized changes to validation rules. Further, as XML Schema are XML documents themselves, they may be managed by XML authoring tools, or through XSLT."

Part 1 abstract: "XML Schema: Structures specifies the XML Schema definition language, which offers facilities for describing the structure and constraining the contents of XML 1.0 documents, including those which exploit the XML Namespace facility. The schema language, which is itself represented in XML 1.0 and uses namespaces, substantially reconstructs and considerably extends the capabilities found in XML 1.0 document type definitions (DTDs). This specification depends on XML Schema Part 2: Datatypes.

From the Part 1 purpose statement: "The purpose of XML Schema: Structures is to define the nature of XML schemas and their component parts, provide an inventory of XML markup constructs with which to represent schemas, and define the application of schemas to XML documents. The purpose of an XML Schema: Structures schema is to define and describe a class of XML documents by using schema components to constrain and document the meaning, usage and relationships of their constituent parts: datatypes, elements and their content and attributes and their values. Schemas may also provide for the specification of additional document information, such as normalization and defaulting of attribute and element values. Schemas have facilities for self-documentation. Thus, XML Schema: Structures can be used to define, describe and catalogue XML vocabularies for classes of XML documents. Any application that consumes well-formed XML can use the XML Schema: Structures formalism to express syntactic, structural and value constraints applicable to its document instances. The XML Schema: Structures formalism allows a useful level of constraint checking to be described and implemented for a wide spectrum of XML applications. However, the language defined by this specification does not attempt to provide all the facilities that might be needed by any application. Some applications may require constraint capabilities not expressible in this language, and so may need to perform their own additional validations."

Part 2 abstract: "XML Schema: Datatypes is part 2 of the specification of the XML Schema language. It defines facilities for defining datatypes to be used in XML Schemas as well as other XML specifications. The datatype language, which is itself represented in XML 1.0, provides a superset of the capabilities found in XML 1.0 document type definitions (DTDs) for specifying datatypes on elements and attributes."

Part 0 abstract: "XML Schema Part 0: Primer is a non-normative document intended to provide an easily readable description of the XML Schema facilities, and is oriented towards quickly understanding how to create schemas using the XML Schema language. XML Schema Part 1: Structures and XML Schema Part 2: Datatypes provide the complete normative description of the XML Schema language. This primer describes the language features through numerous examples which are complemented by extensive references to the normative texts."

W3C has also provided for the creation of a W3C XML Schema Test Collection, announced by Henry S. Thompson (University of Edinburgh and W3C; Oriol Carbo, University of Edinburgh and W3C). "Goals and Objectives: The W3C XML Schema Test Collection work aims at coordinating test suites for W3C XML Schema processors created by different developers." The main objectives as announced 2001-05-02 are: (1) to integrate existing tests for W3C XML Schema processors in a common environment so they can be accessed publicly and shared among developers; (2) to establish a standard approach to test material IPR which meets the needs of both contributors and users; (3) to collect and develop tools to automate the execution and presentation of the test suites; (4) to offer a standard description of tests related to W3C XML Schema processors: [...]; (5) [to provide test descriptions] understandable by a developer without the need to actually view the test file(s) themselves); (6) to offer a standard presentation of test results; (7) to design additional tests and add/regularise descriptions of the existing tests; (8) in due course, to provide an XSLT-based approach to comparing XML representations of the post schema-validation infoset as produced by different processors; we will shortly announce the availability of XML Schemas for both the ordinary Infoset and the PSVInfoset. "The W3C expects to author only a small part of the collection -- we are counting on Member organisations and others to contribute the majority. To offer materials for the collection, please send e-mail to"

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