[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: XML query language
Oren Ben-Kiki wrote: > > Paul Janssens <paul.janssens@s...> wrote: > >In my opinion, an xml query language should only describe a set of > >equations, an xml query language implementation should only solve these > >equations, and whatever is done with the result is NO business of the > >query language. > > Just to make sure I follow: you'd prefer that there would be a standard > <xql:result> DTD, so that results would always be created in an XML format > containing references to the matched XML elements (XLink/XPointer?). The > user would then filter this through XSL or whatever to display the results. correct > Nice separation of concerns, but I see several objections: > > - Efficiency. Suppose I'm querying a very large DB, and I'm getting a list > of matches scattered all over the place. In the current approach, the DB > would both resolve the matches and extract the necessary data, potentially > at the same pass using a lot of locality-of-reference optimizations. In your > method a second tool would re-fetch the references in a second phase, which > would probably double the cost of doing the query. That's an implementation issue. You can build a tool that has an input of both the query and the style description, and optimizes the DB acces. In other words xml report syntax = xml query syntax + xml style syntax does NOT imply xml report implementation = xml query implementation + xml style implementation > - Power. Assume that I hypnotize all the W3C members to adopt the XSL > transformational part as XQL version 1.0 :-) This is more powerful then > current ?QL proposals because it allows for an <xsl:template> to call > <xsl:apply-templates> - that is, to perform nested queries (and therefore, > BTW, offers a natural way to do joins without variables, and solves other > ?QL problems). All this works because XSL has a rich language for > constructing the results. In your approach, you won't be able to do a lot of > that; you'd end up adding special constructs for them, duplicating XSL's > capabilities in an incompatible language. Of course you'd be in good > company - that is what all the other ?QL language proposals do :-) I have no problem with recycling some XSL syntax into ?QL where applicable, in fact it would be a good idea. Just as you could recycle XPointer syntax where applicable. > - Convenience. It is easier to specify a query as just "one thing" instead > of two. Note that even if ?QL == XSL transformation, it still makes a lot of > sense to filter its results through another XSL stylesheet for presentation > in most cases. Even lazy users will do so - if, for example, they had > already available XSL sheets for displaying certain types of results. The report syntax will allow you to either link to a query and style, or describe them inline, e.g. <report> <query>... </query> <style>... </style> </report> Paul Janssens - paul.janssens@s... xml-dev: A list for W3C XML Developers. To post, mailto:xml-dev@i... Archived as: http://www.lists.ic.ac.uk/hypermail/xml-dev/ and on CD-ROM/ISBN 981-02-3594-1 To (un)subscribe, mailto:majordomo@i... the following message; (un)subscribe xml-dev To subscribe to the digests, mailto:majordomo@i... the following message; subscribe xml-dev-digest List coordinator, Henry Rzepa (mailto:rzepa@i...)
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