Re: Why doesn't XML have Bag?
* Roger L. Costello | | Then let me ask another question - why do DTDs not allow me to specify | an unordered list of elements? For example, | | <!ELEMENT Kitchen RDF:Bag(Sink, Stove, Refrigerator)> | | With this notation I am trying to indicate that an XML document that | conforms to this DTD must have a <Kitchen> element which has three child | elements - <Sink>, <Stove>, and <Refrigerator>, and these child elements | can be in any order. Isn't this a useful thing? Sure it is, and SGML has it already: <!ELEMENT Kitchen (Sink & Stove & Refrigerator)> | I gather from your message that you are saying that it is not a | limitation of XML, but rather a limitation of DTDs? It is a limitation of DTDs and was introduced because without this operator element content models are easily mapped to finite state automatons, but the introduction of the '&' separator makes automaton generation much more difficult. Existing SGML parsers already do this, and there are some research papers giving algorithms for this, but the designers felt that this was one of the things that would have to go in the simplification from SGML to XML. | How about DCDs? DCDs have no official standing, they're just a proposal to the W3C. XML Schemas, when they are defined, may (or may not) have this for all I know. If they do we might as well add it to DTDs too. --Lars M. 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/ and on CD-ROM/ISBN 981-02-3594-1 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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