[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: XML spec and XSD
At 2009-11-15 07:34 +0530, Mukul Gandhi wrote: >On Sun, Nov 15, 2009 at 2:15 AM, Tim Bray <Tim.Bray@sun.com> wrote: > > I thought Rick was being fair. Â XSD is a failure by any sane technical > > measure. > >I agree, that XSD spec has been quite mammoth and functionally >complex. That's the only aspect, I see XSD being different from most >of other W3C specs. I wouldn't agree with that. I also side with Tim and Rick and others who grudgingly find they have to work with XSD (usually to meet customer requests; personally I migrated from DTD to RELAX-NG and never embraced XSD), and for the same reason that Tim cites above: technical issues. Size and complexity are not, necessarily, technical faults. > From functional point of view, I don't think XSD doesn't work. There are a number of areas that are problematic. One example is no two vendors have implemented "redefine" the same way. I had researched this to meet specific requirements identified for the UBL project and was burned by assuming the way one processor implemented redefine was the way others implemented it. >So many numerous XML applications currently used XSD. Popularity is no measure of functionality. Vendors who are pushing XSD products would likely tell their clients there are no other choices for schema languages. It is my assessment that vendors and users ignore or are unaware of other sources of XML-based technologies, such as ISO/IEC JTC 1/SC 34 which created the ISO/IEC 19757 Document Schema Definition Languages (DSDL) that includes RELAX-NG, Schematron and NVDL among other XML specifications. >I don't think, there is anything wrong with the basic core/philosophy >of XSD. An example of a core fault is that W3C Schema is not closed under union. I cannot programmatically express the union of two XSD schemas to create a third XSD schema that validates instances of the other two. I might be able to by hand, but not programmatically. This is not academic: consider an XML document where in two different contexts there is an element <x> with different content models. I then write a query that assembles all of the documents <x> elements under a single parent result element. I have to hand-craft the schema that validates the result of the query (if it is possible and not an ambiguous content model), as I cannot express in XSD-speak two sibling elements with different content models. If I could simply express the union of the two original <x> content models as the content model for the query result <x>, then I wouldn't have to resort to hand-crafting. There may be other "core" faults, but that is one that has been a problem for me. In RELAX-NG compact syntax, if I have a grammar "a" and a grammar "b" (be it document level, element level or any level of a grammar; at the element level both grammars might express different content models for the element <x>), the union of these two grammars is expressed as "a | b". No other work is necessary. An instance of <x> will validate true if it passes the constraints expressed by either grammar. >I guess, some of users who don't like XSD generally, it's >probably because of it's huge size, and steep learning curve. But cognoscenti such as Rick Jelliffe, Tim Bray and many others would not find a specification's huge size and steep learning curve a fault if, technically, the end result was something that worked well. It might indeed be a barrier for new people to W3C Schema, but my recollection is that negative opinions in this debate have not come from representatives of that user group. >I believe, XSD also get's functionally better with the upcoming 1.1 release. Probably the functionality will be better, yes, but will it address everything? We won't know until it is released, and I suspect some legacy 1.0 issues will dog all dot-releases of XSD. I hope this is considered helpful to the discussion. . . . . . . . . . . . Ken -- Vote for your XML training: http://www.CraneSoftwrights.com/x/i/ Crane Softwrights Ltd. http://www.CraneSoftwrights.com/x/ Training tools: Comprehensive interactive XSLT/XPath 1.0/2.0 video Video lesson: http://www.youtube.com/watch?v=PrNjJCh7Ppg&fmt=18 Video overview: http://www.youtube.com/watch?v=VTiodiij6gE&fmt=18 G. Ken Holman mailto:gkholman@CraneSoftwrights.com Male Cancer Awareness Nov'07 http://www.CraneSoftwrights.com/x/bc Legal business disclaimers: http://www.CraneSoftwrights.com/legal
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