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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: Can XML Schemas Support Document Systems (WAS RE: ZDNet Schema artic
 First of all, i personally think most of the stuff are not hard to understand -- if they are hard to understand, then we can very well suspect their correctness. XML Schema might be able to support document systems, but I have not seen a single operation defined for xml schema. let me give one simple example -- consider a system that does the following -- it performs some select operations on the documents, returns the result document and also the result schema. I think such a system is not definable at this point of time using XML schema. to elucidate a bit further -- what can happen is the output schema can be something like a) (book*, author*, book*), b) (book1*, book2*) etc both of which cannot be defined using xml schema -- note that the first is what "we" call horizontal ambiguity/non-determinism, and the latter is what we call vertical ambiguity/non-determinism. If you want to get into the "gory" details, i might recommend one of my own work -- "Reasoning about XML Schema languages using formal language theory" -- it is published as an IBM Technical Report -- available at http://www.cs.ucla.edu/~dongwon/paper -- personally I think almost all aspects of it is *quite* important. When we start off with some implementations of such systems, we might think it works -- but suddenly we get bad examples, and "unexpected things happen" -- if we did not recognize this non-closure and somehow handle this. once again some history and also this might seem slight digression -- but regular tree grammars and local tree grammars have been *widely* studied for a very long time (local tree grammars were definitely studied in 75). they are very clean mathematically -- local tree grammars are not closed under several operations, but we can easily define most operations -- Makoto Murata has studied them. XML Schema, i am not sure how we are going to go about defining operations. First thing probably is define union for XML schemas. I might take a hint from history that local tree and regular tree grammars are definitely mathematically precise and more interesting than the types of grammars defined by XML Schema -- which does not conform to either. regards - murali. On Wed, 25 Apr 2001, Bullard, Claude L (Len) wrote: > On the other hand, I am interested in the assertions > that XML Schema cannot support document-centric applications. > It appears to me that it can if the right set of features > are used, but maybe I am missing something more vital than > "it's hard to understand". > > Can anyone summarize the position that it can't support > these systems? > > Len > http://www.mp3.com/LenBullard > > Ekam sat.h, Vipraah bahudhaa vadanti. > Daamyata. Datta. Dayadhvam.h > > ------------------------------------------------------------------ > The xml-dev list is sponsored by XML.org, an initiative of OASIS > <http://www.oasis-open.org> > > The list archives are at http://lists.xml.org/archives/xml-dev/ > > To unsubscribe from this elist send a message with the single word > "unsubscribe" in the body to: xml-dev-request@l... > 
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