Re: Fw: XML query language
Oren Ben-Kiki <oren@c...> wrote at 31 Mar 99, 12:12: > Paul Prescod <paul@p...> wrote: > >I wrote: > >> Well, them, what other way is to return a list of XPointers then to store > >> each in an "element"? > > > >You don't need an element. You just need a nodelist. Look at the DOM's > >brutally named "getElementsByTagName" method. What a XML query should return depends on what the results are needed for. There is no such think as "the right way" to use an XML query language. Look who was on the W3C-QL workshop '98 and what they asked for: 1. Information Retrieval XML seen as: Collection of text documents Formalisms offered: Z39.50, RDF, WebSQL, PAT, ... Query result needed: References to relevant documents 2. WWW information systems XML seen as: Abstraction of heterogenous data sources and services Formalisms offered: HTTP, CGI, URI Query result: Integrated data sources and services 3. Database community (both rleational and OO): XML seen as: Set of structured facts (order doesn't matter) Formalisms offered: SQL, OQL Query result: Set of (re)structured facts (order doesn't matter) 4. Document processors XML seen as: Structured text (order matters) Formalisms offered: XSL selectors, Query result: Pointers to selected text fragments (order matters) for further processing (e.g. by XSL templates or programming languages) 5. Document transformation XML seen as: Syntax tree Formalisms offered: hedge automata Query result: Transformed syntax tree 6. Hypertext community XML seen as: Graph of structured nodes connected by Hyperlinks Formalisms offered: XLink, XPointer Query result: Locations within a structured node All of those need a QL. But all have different constraints (e.g. Hypertext needs a QL to fit in URL) and want different results (pointers to documents vs. documents vs. restructured documents). David Maier identified five fundamental operations in XML queries: 1. Selection of elements depending on content, structure or attributes 2. Extraction of elements 3. Redution of elements 4. Restructuring of documents 5. Combination of elements Looking at the user groups, e.g. neither Hypertext nor information retrieval will need restructuring or combination. Document processing will need all 5 operations. Right now XQL offers operations 1-3, XSL offers operations 1-4 and XML-QL offers operations 1-5 (with the cost of loosing order). You suggest to use XPointers as the result of XML queries. XPointers from my point of view are queries by themselves. Being from the database community, I want restructured XML as a result. Who is right ? No one. It just depends on the way you look at it. ++im -- Ingo Macherius//Dolivostrasse 15//D-64293 Darmstadt//+49-6151-869-882 GMD-IPSI German National Research Center for Information Technology mailto:macherius@g... http://www.darmstadt.gmd.de/~inim/ Information!=Knowledge!=Wisdom!=Truth!=Beauty!=Love!=Music==BEST (Zappa) 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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