[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] XSchema Specification - Introduction (Section 1, Version 4)
Remember this, from a long long time ago? It's the XSchema introduction, freshly revised with a list of contributors. As always, a prettier HTML version of this will be posted shortly at http://purl.oclc.org/NET/xschema. Please note that I am changing email addresses. Please address future XSchema correspondence to simonstl@s.... (The old address will work as well as it ever did - poorly - but I won't be checking it as often.) Simon St.Laurent Dynamic HTML: A Primer / XML: A Primer / Cookies 1.0 Introduction In order for document processing to be reliable, it is necessary to be able to describe classes of documents and to verify individual documents' membership in these classes -- in other words, to be able to express constraints on documents and thus define 'document types'. XML inherits a mechanism for doing this from SGML: the Document Type Definition. XML DTDs can perform a subset of the functions of SGML DTDs. DTDs have limited expressiveness and it is necessary to experiment with new ideas in schema design. These ideas include a syntax that is more like that of XML document content, certain kinds of extensibility and a cleaner separation between parsing and verifying. XSchema is an experimental schema language designed to provide a starting point for these experiments. So that XSchemas will be immediately useful with existing software, the XSchema specification will describe a conversion from XSchema documents to DTDs. This initial version of the XSchema specification is deliberately simple, providing an initial base for implementations while introducing as few complicating factors as possible. Authors accustomed to DTD creation will find their toolset constricted; it is hoped that supporting software and tools available from other standards will make up for this reduced toolset. 1.1 Status The XSchema specification is the product of discussions on the xml-dev mailing list. This document has no official status. The editors have no affiliation with the World Wide Web Consortium (W3C), the organization developing and maintaining the XML standard, nor any affiliation with any W3C member organizations. While it is hoped that this document may eventually be submitted to the W3C as a Note, it is not an official specification and should be considered experimental. 1.2 Origin and Goals Proposals for describing SGML document type definitions using document syntax rather than the separate declaration syntax have been under development for a number of years, and used by several tools for documentation. The current proposal arose from a number of concerns surrounding XML's usability and consistency. Originally conceived of as a mapping of DTD syntax to document syntax, the project has developed into an effort focused on creating schemas describing element and attribute structures rather than preserving every function provided by XML 1.0 DTDs. The list of goals developed by the xml-dev discussion follows: 1. XSchema documents shall use XML document syntax, using element nesting and attributes to describe all constraints that may be verified by a processor using XSchema . 2. XSchema shall define a transformation from XSchema documents to DTDs. 3. XSchema documents shall be capable of representing the normalized element and attribute structures defined in XML 1.0 DTDs, and provide namespace support. 4. XSchema documents shall be parseable, manageable, and manipulable using the same tools used to parse, manage, and manipulate XML documents. 5. XSchema documents shall be easy to create, read, and modify, and shall provide authoring support for XML documents. 6. XSchema documents shall be easy to use in combination with a parser to provide structural validation of documents. 7. XSchema shall include an XSchema document and an XML 1.0 DTD defining the structure of XSchema documents . 8. XSchema shall suggest mechanisms for applying XSchema documents to documents. 9. XSchema shall include mechanisms for extending the information included in XSchema documents to support metadata. 10. The XSchema specification shall be readable, clear, and rigorous, using terminology and nomenclature as close to the XML 1.0 specification as possible. 11. The XSchema specification will comply with and be consistent with W3C recommendations. 12. XSchema documents shall provide constructs for human- and machine-readable documentation. 1.3 Relation to Standards XSchemas use XML 1.0 document instance syntax and may be applied to XML 1.0 documents. XSchemas are also designed to make use of XML namespaces. It is hoped that XSchemas and RDF Schemas may be mapped to each other. This specification has also been influenced by the discussion of the XML-Data proposal made to the W3C on 5 January, 1998. XSchema also refers to several IETF standards, notably Multipurpose Internet Mail Extensions (MIME). 1.4 Terminology The requirement levels used throughout this document reflect the approach of RFC 2119 (http://www.isi.edu/in-notes/rfc2119.txt), though keywords (like may and must) are not capitalized. Other terms used are defined in the XML 1.0 Recommendation, available at http://www.w3.org/TR/1998/REC-xml-19980210. 1.5 Authors and Contributors The XSchema specification is the result of contributions from a large number of people on the XML-Dev list, coordinated by a smaller group of authors. Authors: Simon St.Laurent Ron Bourret John Cowan Contributors: Paul Prescod Peter Murray-Rust Alain Deseine Chris Maden Rick Jelliffe Toby Speight Jeni Tennison Marcus Carr Michael Kay James Anderson David Megginson Don Park James K. Tauber Tim Bray John Simpson Steven Champeon Andrew Layman Arjun Ray Curt Arnold Bill la Forge Bryan Gilbert Carl Hage Dan Brickley David Brownell David G. Durand David Ornstein David Rosenborg Eric Albright Francis Norton Frank Boumphrey Gisli Olafsson Dirk Gouders Guy Huard Jacek Ambroziak Jack Bolles Jarle Stabell Jeremy H. Griffith Jon Bosak Lars Marius Garshol Liam Quin Lisa Rein Mark D. Anderson Matt Mower Matthew Gertner Mark Tucker Kenneth J. Meltsner Murata Makoto Murray Maloney Parameshwor Karki Paul Haahr Paul Rabin Robin Cover Scott Vanderbilt Sean McGrath Simon North Stefan Wagner Steve Withall Steven R. Newcomb Thuy-Lin Nguyen Todd Ross W.E. Perry Will Hunt Simon St.Laurent Dynamic HTML: A Primer / XML: A Primer / Cookies xml-dev: A list for W3C XML Developers. To post, mailto:xml-dev@i... Archived as: http://www.lists.ic.ac.uk/hypermail/xml-dev/ To (un)subscribe, mailto:majordomo@i... the following message; (un)subscribe xml-dev To subscribe to the digests, mailto:majordomo@i... the following message; subscribe xml-dev-digest List coordinator, Henry Rzepa (mailto:rzepa@i...)
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