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Thanks Dave for clarifying terminology. It is "set" that I meant, not "bag". Just to make certain that I understand, an XML DTD cannot express the following: "A <Kitchen> element contains exactly three child elements: one instance of <Sink>, one instance of <Stove>, and one instance of <Refrigerator>, and these child elements can appear in any order." Correct? /Roger P.S. Attributes can be listed in any order in an XML document, regardless of the order that they are listed in the DTD. Right? David Megginson wrote: > > Roger L. Costello writes: > > > Why doesn't XML support the notion of an unordered list of elements, > > i.e., a Bag? Perhaps this is a limitation of DTD, not XML? That is, > > DTDs do not support Bags, but XML has no such inherent limitation? Does > > DCD support Bags? /Roger > > XML DTDs can constrain the content of a bag just fine: > > (a|b|c|d|e|f)* > > XML DTDs cannot constrain the content of a set (where each element may > appear exactly once, in any order). This is not an SGML DTD > limitation, since in SGML you can use > > (a&b&c&d&e&f) > > You can simulate this in XML DTDs, but the content models become > absurdly large. > > This is not to say that you cannot have a set in XML even *with* DTD > validation; it's just that DTD validation will not catch the errors. > For example, either > > (a|b|c|d|e|f)* > > or even > > ANY > > will allow a set, but they will not catch the error where the same > element appears twice. > > 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/ 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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