- From: <Noah_Mendelsohn@lotus.com>
- Date: Fri, 9 Nov 2001 15:21:27 -0500
- To: Eric van der Vlist <vdv@dyomedea.com>
- Cc: xmlschema-dev@w3.org
Thank you for your comments. Personally, I share some of your concerns regarding the exact tradeoffs made in the extension/refinement space (though I do like the separation of the basic concepts). One of the tricky things in doing a design like this is to know what to do when various constituencies strongly indicate they need a feature, as was the case with this single-inheritance, sequence-based form of extension. As I sometimes have said, large committees tend to produce large languages. Regarding systems like Schematron that can do more elaborate constraint checks and in that sense are more expressive: they are very interesting systems, but I think Schematron in particular represents a significantly different point in the design/performance space. I think I know how to optimize XML schema validation a lot more aggressively than I would suspect is possible with Schematron. I could be wrong, but that's my intuition. For high performance eCommerce scenarios, that's important. I also agree in general on composability (is that a word?). On the other hand, one thing that's made XML 1.0 an interop success is that there isn't much optionality in it. You either understand well-formed or you don't. There are, of course, a few major choices such as whether you are DTD-aware and whether you validate. But mostly, all processors handle all XML. In the case of schema, the more we rely on composition to build the language, the greater the chance that I send you a schema that's perfectly legal, but that you can't handle (because I composed features that you don't support). I'm not sure we shouldn't wrap up this discussion, before it bothers the list with a huge discussion of all the tradeoffs made in the schema language. Anyway, the above would be my reactions to the specific points that you've raised (and by the way, your little O'Reilly book on schema is very cool!) Thanks. ------------------------------------------------------------------------ Noah Mendelsohn Voice: 1-617-693-4036 Lotus Development Corp. Fax: 1-617-693-8676 One Rogers Street Cambridge, MA 02142 ------------------------------------------------------------------------ Eric van der Vlist <vdv@dyomedea.com> Sent by: xmlschema-dev-request@w3.org 11/09/01 03:00 PM To: xmlschema-dev@w3.org cc: (bcc: Noah Mendelsohn/CAM/Lotus) Subject: Re: Rationale for restricted uses of "all" Hi Noah, Noah_Mendelsohn@lotus.com wrote: Thanks for sharing this insight with us! ... > Just to avoid complicating an already overly large > specification, we decided to tackle extension initially only for > sequences, which models certain forms of OO single inheritance moderately > well. I think that this is the main point and what I find most questionable about W3C XML Schema is not the fact that it's not complex enough ;=) but rather the "usage" made of the complexity accepted into the language... Of course it's easy to criticise and most of what I have learned about schema languages have been learned studying the work of the Schema WG... but if I may be allowed one more critic, I would say that there are 2 directions in which complexity can be deploied when defining a schema language: the first one is the expressive power (ie the scope of the set of instance documents which can be described) while the second are the "composing features" which let users recompose basic building blocs. IMHO, the level of overall complexity would have been better used by focussing more on the expressive power than on the "composing features". Expressive power is the "engine" or the basis of a schema language and you can't improve it afterward, while you can always add more "composing features" which I see more like a cherry on the cake... Anyway, it's now the way it is ;=) and for the best or the worse I guess we have to live with it for a while and try to use it for the best! Thanks Eric -- Rendez-vous à Paris pour le Forum XML. http://www.technoforum.fr/Pages/forumXML01/index.html ------------------------------------------------------------------------ Eric van der Vlist http://xmlfr.org http://dyomedea.com http://xsltunit.org http://4xt.org http://examplotron.org ------------------------------------------------------------------------
Received on Friday, 9 November 2001 15:31:47 UTC