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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: a or b or both - mystery..
 I think TREX is largely motivated to allow people to express what they want more easily -- in short, it has so few restrictions that we do not have to worry whether our schema is correct or not. I think almost all other schema languages have more restrictions than TREX. But I think RELAX has its own advantages -- it clearly separates "types" that produce trees, and types that produce "hedges" - hedge is an ordered list of trees (Makoto is the expert in this field). I think this separation is very clean. I have asked professors and others -- everyone I have asked believes things just will not work without closure - you will get unexpected things. I think if you use XML only for data exchange, then closure does not matter, but if you want to do actual processing, then I think closure is *very* important. If I am right, a good example of a simple query that is not closed for XML schemas is given in the reference. In short, non-closure I think is a *very* serious issue -- I have verified with a few XML people also, but still I am not sure if there is universal consensus that closure is very important. Regarding the project that I work on, I do *union* of schemas *vigorously* -- for RELAX union is very clearly defined, I am not sure whether it will ever be possible to define a meaningful union for XML Schema. It might be possible to get a very good closed set of operations for XML Schema, but I doubt it very much. This is based on what I have seen so far, and based on history. I say history because languages such as RELAX and TREX form regular tree languages, and they are studied from late 1950's -- they are *very* well studied. And it was a pleasure trying to explain whatever I know. I think everyone in this group tries to learn from the other. Also this mailing list helps a lot in trying to understand XML as a group. I have tried my bit before to persuade XML Schema to consider regular tree languages, but I think they might not have -- so to get a clear picture, we probably should get the views of the XML Schema WG also. <warning>speaking for himself only</warning> cheers - murali. On Tue, 17 Apr 2001, Marcus Carr wrote: > > Murali Mani wrote: > > Is "ease of use" the main motivation for allowing non-deterministic > models in TREX? As these problems seem even less frequent in XML than > they did in SGML, this seems not to buy a whole lot. > > > PS: The issues are not just expressiveness when you get to document > > processing, but closure properties are *very* important, and it gets > > really messy as XML Schema is *not* closed under 99% of the operations > > that anyone will need. > > You clearly understand this stuff a lot better then I do, so please > interpret any questions as curiousity rather than a challenge to your > points. To whom are closure properties important? What proportion of > developers will be impacted by the lack of closure, and what will the > ramifications be? Do the restrictions on queries due to lack of > closure result in processing inefficiencies, or something more dire? > Would you term this as a wide issue, or a narrower one that you're > looking at very closely? > > > I am not sure whether I should give this, but I think this is a decently > > prepared report, written largely by my friend, but it is my work also, I > > think some people might find it useful -- it is available at > > http://www.cs.ucla.edu/~mani/xml/papers/conferences/WebDB2001/td-main2.ps > > It looks very interesting, but it would help me if I understood the scope of the > issues better. Thanks for your patience. > > > -- > Regards, > > Marcus Carr email: mrc@a... > ___________________________________________________________________ > Allette Systems (Australia) www: http://www.allette.com.au > ___________________________________________________________________ > "Everything should be made as simple as possible, but not simpler." > - Einstein > > > > ------------------------------------------------------------------ > 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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