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> -----Original Message----- > From: Murali Mani [mailto:mani@C...] > Sent: Monday, April 23, 2001 9:27 PM > > SQL has a nice math based on relational algebra/calculus. > The truth is XML Schema does not have this. > Actually probably because of my strong bias, but I believe XML Schema > defies math -- for an example, XML Schema defies XDuce. > But this is true -- the math for RELAX/TREX was first studied in the > late 1950's, and it has *very* strong math. Interestingly, the Schema Working Group is/was? trying to develop a formalism upon which to base the syntax. See http://www.w3.org/TR/2001/WD-xmlschema-formal-20010320/ There are a number of "infidelities" between the spec and the formalism, however. For some reason, the WG appear to have decided that these are bugs in the FORMALISM rather than problems lurking in the spec. (The unsanitized formalism draft at http://www.wavelet.org/cm/cs/who/wadler/papers/msl/msl.pdf calls them "problems with XML Schema", the public draft on the W3C site calls them features that are "not currently modelled.") As depressing as it is to be reminded of all this <grin>, I think you've hit upon an important answer to my original question: User-friendly interfaces can hide TEDIOUS FORMAL DETAILS of a spec that no sensible user would ever want to touch (e.g. a fax machine hides the CCITT image compression specs from the person pressing the buttons, and SQL hides the formalisms of the relational algebra). But it's not at all clear that they can hide conceptual complexity (and perhaps ambiguity) such as the XML Schema restriction rules. To quote from the (un-sanitized) schema formalism paper referenced above, "An attempt at defining formal rules corresponding to the definition of restriction required more than 100 lines of formal rules (as compared to the one-line definition given in the current document). Many rules had five or six premises." Something tells me that we're not going to see a clean, user-friendly interface that encapsulates these 100 rules from Microsoft or anyone else.
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