RQTS : tag order

Robert A. (Bob) Morris ram at CS.UMB.EDU
Mon Dec 13 11:10:49 CET 1999

Gregor Hagedorn writes:
 > Date:         Mon, 13 Dec 1999 16:21:15 +0100
 > From: Gregor Hagedorn <G.Hagedorn at bba.de>
 > To: TDWG-SDD at usobi.org
 > Subject:      Re: RQTS : tag order
 > Bob Morris wrote:
 > > Here's a proposed requirement for data exchange, brought home by one
 > > of Leigh's examples:
 > >
 > > <RQT> It should be possible from the data itself, perhaps together
 > > with external resources to which it refers, for software to determine
 > > whether the order matters for any collection of tags in the
 > > data.</RQT>
 > I agree, especially that the software should be able to determine it.
 > Regarding XML, tags, and DTDs, I believe, the assumption is that
 > order does not matter, wherease an order can be imposed on attributes
 > within a tag, correct?

No, it is exactly the opposite. A DTD imposes an order on tags, but attributes
are unordered.

However, the November 5 working draft of XML Schema provides
mechanisms for settling tag order questions. XML Schema is a language for
specifying tag constraints in XML itself, rather than in the DTD
language which is not itself a special case of XML. Among other
things, it provides strong data typing, including the ability to
restrict the range of data, whereas in a DTD the only primitive data
type is a string.

It is slightly plausible that XML Schema would actually provide a good
data modeling language independent of whether one wished to use it as
an interchange language or as the native data store.

Bob Morris

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