RE: Schemas and Other Crucial XML Questions
Sam Gentile writes: > We mean just the XML data coming into the parser (coming over the > wire). I guess we could call it an XML file. OK, now I understand what you mean -- according to the spec, you're referring to an 'XML document', though I know that the term will sound strange to database-oriented people (XML takes a very docu-centric view of things). > Sam Gentile writes: > > We have a spec called "XML-Data W3C Note 05 Jan 1998", which > > discusses schemas. It is not clear from the document what a > > schema is used for or what it's purpose is. Is it for designing > > the XML buffer only or is it read by the parser? Is it an > > extension to XML? Are they even necessary in basic XML? XML-Data is a note that was submitted to the W3C by Microsoft and a couple of partners -- it has no official status (a W3C "Note" means roughly "here's a neat idea from one of our members"). XML 1.0 DTDs and proposed replacements/enhancements such as Microsoft's XML-Data and XML-Dev's XSchema perform three distinct roles: 1. Provide a schema for validating the *logical structure* (element/attribute/data) structure of an XML document; as a side effect, structural schemas can also provide enough information to control a guided XML authoring tool. 2. Declare the entities (internal strings or external objects) that make up the *physical structure* of an XML document. 3. Provide default logical content for an XML document (such as default values for attributes, though XML-Data goes further). Some people have argued -- quite convincingly, I think -- that these roles should be kept separate: they are mixed together right now for historical compatibility with ISO 8879:1986 DTDs. It is important to note that the W3C's XML WG will soon begin work on structural schemas and data typing, and that eventually a new W3C standard will appear -- until then, the only W3C standard for structural schemas is XML 1.0 DTDs, and XSchema or XML-Data should be considered strictly experimental. > > Also, we have been hearing rumors of a "short" XML notation. Is > > there one? We have a need to reduce the size of our buffers. No, there is no such thing. XML's parent, SGML, included extensive facilities for markup minimisation and has suffered badly for it, since SGML tools are far too difficult to write (there is still not a single Java-based SGML parser, beside probably more than a dozen Java-based XML parsers). There are, however, alternatives: for example, you could compile the XML to a compact binary format for internal storage then decompile it back to a verbose format for export -- there's no requirement to store it internally as text. All the best, David -- David Megginson david@m... http://www.megginson.com/ 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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