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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: Why XML data typing is hard (was Re: Internal subset equivalent in n
 At 98/11/27 16:17 +0100, Ketil Z Malde wrote: ><david@m...> writes: > >> The real question, though, is how constraints could be enforced. >> Let's start with an extremely simple example: > >> <value xml:type="float"></value> > >Now you're adding type information to the content, what I suggested >was to constrain *form*. For one thing, I would not specify this in >the document (this is just a gut feeling, but why would you?), I would >specify it in the DTD, e.g. like so: > > <!element value #REGEXP:"-?[0-9]*.[0-9][0-9]"> > >(or some such, you get the point). > >> What are the allowed contents? > >Then the document could contain > > <value>4.50</value> > <value>-0.01</value> or > <value>.00</value> > >but not > > <value>1.0</value> or > <value>4,50</value> Then your example proposed range of values is inappropriate because "4,50" is a valid float from an I18N point of view. In Canada, valid expressions of currency numbers are $1.47 or 1,47$ based on where you are. The decimal separator is "." in English Canada and "," in French Canada. I understood David's point to be that two valid expressions of the same float aren't lexically the same. >> <value xml:type="float">1,5</value> >> <value xml:type="float">1.5</value> > >This won't be a problem, if the DTD specifies what can the processing >software should expect. You could even validate processing software >to some extent. And I suppose your regular expression example could be changed to <!element value #REGEXP:"-?[0-9]*(\.|,)[0-9][0-9]"> Currency values would need a larger expression. I gather from Michael S-McQ in a presentation in Chicago that the regular expression for a valid date (taking into account days of the month and leap years) is 4801 characters long. Since these values themselves are hierarchical, one could model the example as: <whole>4</whole><part>50</part> but one couldn't do that with the separate elements <year>1998</year><month>02</month><day>29</day> and know it was invalid without the concept of the set representing a valid date. >I think trying to define some set of types to be used in *all* XML >documents is taking the wrong approach. I don't really see this as >either workable or desirable. What would the point of using xml:type >be? Perhaps to abstract what is being expressed in markup to allow different lexical expressions of the same value to be considered valid. ............ Ken -- G. Ken Holman mailto:gkholman@C... Crane Softwrights Ltd. http://www.CraneSoftwrights.com/x/ Box 266, V: +1(613)489-0999 Kars, Ontario CANADA K0A-2E0 F: +1(613)489-0995 Training: http://www.CraneSoftwrights.com/x/schedule.htm Resources: http://www.CraneSoftwrights.com/x/resources.htm Shareware: http://www.CraneSoftwrights.com/x/shareware.htm 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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