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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: XQuery types was Re: Yet another plea for XUpdat
 Before this turns into a pointless critique of the XQuery formal semantics I'll just steer this conversation back to the original point. Some members of the XQuery WG feel that a complex type system such as XQuery's is necessary for updates while I am of the opinion that a post-validation requirement is the minimum that should be required. The bottom line is that any XML database product that supports XQuery and W3C XML schema plus an update capability will have to support post-update validation because the XQuery and W3C XML Schema "type" systems leave the door open for too many things to be dynamic. By the way here are some quotes from the Formal Semantics document which point out what I mean by validation vs. type system "The XQuery type system is based on XML Schema. XML Schema defines a notion of validation for XML documents. When doing validation, an XML Schema processor checks if the structure, and the text content of a document verifies the constraints on the structure, and the constraints on values, specified in the schema. As an example of constraints on the document structure, all book elements might be declared to contain an isbn attribute, and a title element, followed by a sequence of one or more author elements. As an example of constraints on values, the isbn attribute might be declared as a subset of the XML Schema xsd:string values, using a XML Schema pattern facet." Especially with regards to restriction facets, there simply is no way for this to be implemented without something akin to post-update validation. Identity constraints as well. In fact, when I think about even making sure that the results of an update do not result in an invalid content model for an element in the document is pretty much another validation issue not a type one. --- Jonathan Borden <jborden@a...> wrote: > Dare Obasanjo wrote: > > > > Amusingly enough, my day job requires me to be > familiar with both > aforementioned documents. So what exactly was your > point again? > > I think XQuery semantics is terrific, albeit a bit > technical. I consider it > to define a perfectly reasonable and adequate for > the intended purpuse, type > system, which as is happens is very similar to the > RELAXNG regular > expression syntax, i.e. XQuery types are RELAXNG > regular expressions, and > both use XML Schema for simple (non-XML) datatypes. > > Typing and validation are closely related. Consider > a type as an (usually > unbounded) set whose members are those pieces of XML > that are 'valid' with > respect to the type specification. > > That's exactly my point. > > Jonathan > > > > > Dare Obasanjo wrote: > > > > > Secondly, XQuery doesn't really have a type > system > > > because it uses W3C XML Schema which is a > validation > > > system. > > > > Gasp. As punishment for saying such things you > should be forced to read > > http://www.w3.org/TR/query-semantics/ > > > > Jonathan > > > > > > ----------------------------------------------------------------- > The xml-dev list is sponsored by XML.org > <http://www.xml.org>, an > initiative of OASIS <http://www.oasis-open.org> > > The list archives are at > http://lists.xml.org/archives/xml-dev/ > > To subscribe or unsubscribe from this list use the > subscription > manager: <http://lists.xml.org/ob/adm.pl> > ===== THINGS TO DO IF I BECOME AN EVIL OVERLORD #145 My dungeon cell decor will not feature exposed pipes. While they add to the gloomy atmosphere, they are good conductors of vibrations and a lot of prisoners know Morse code. __________________________________________________ Do You Yahoo!? Yahoo! Health - your guide to health and wellness http://health.yahoo.com 
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