At 17:28 11/09/98 +0200, Ron Bourret wrote: [...] > >I suggest that a short-term solution for the latter is to simply combine >elements from different DTDs as one sees fit. Although the resulting documents >are not valid wrt their original DTDs and cannot be used by DTD-specific >applications, XML does not require valid documents and the use of standard tags >facilitates the search process. I am advocating a certain degree of anarchy >here, but the Web is inherently anarchic and if we wait until we find a way to >combine DTDs without breaking DTD-specific applications, we're missing the >chance to build some extremely useful applications right now. > >(By the way, a nice feature of XML editors that would help this along would be >to read DTDs/schemas from said Yahoo-like repositories, let users insert >elements whereever they want from whatever DTDs/schemas they want, and generate >new DTDs as requested.) > I agree with this. I have written two DTDs in XML (CML and VHG) both of which have to interoperate with other *unknown* DTDs. As a simple example, a paper in chemical physics requires (at least) xHTML, MathML, CML, RDF and DC. It is inconceivable that a generic DTD can be created that has valid content models for all conceivable applications in this domain. [It *is* conceivable that the J.Chem Phys produces a DTD and it's also highly probable that if J. Phys Chem also does it would use a different one.] I cannot see how, except in very carefully regulated domains (such as legal, patent, regulatory) it will be possible to combine generic DTDs to provide a useful mixture. For example, if someone wishes to embed a <price> in a <molecule> this is a perfectly possible and reasonable thing to do. Why should I say they can't? Example: <molecule> <price currency="USD" unit="litre">1.0</price> <atomArray builtin="element">O H H</atomArray> </molecule> This does NOT break my software because it simply scans for things it knows about in content (e.g. <atomArray>). Similarly it's perfectly possible to scan the document with XLink/Xpointer (whenever they get finalised) to find a <molecule> with a descendant of type <price> with attributes of currency. <price> could easily come from a well defined DTD, as will <molecule>. This is - and has to be - the approach that CML takes. So almost all XML-elements will have to have ANY content. This is a pity, because I'd like to be able to insist that <molecule> contained (atomArray)* - yes a molecule without atoms is conceivable. I think that schemas must allow for this - and I believe that XSchema does. The other approach is to allow links - and I really wish that we could see some work going on here. There are two ways - one is to have a link on the molecule, e.g.: <molecule id="H2O" href="price.xml#water">... and the other is to have a link database (I have missed out the other XLink attributes for brevity and because I can't remember the current version of the spec): <extendedLink title="chemical catalogue"> <locator href="molecules.xml#H2O"/> <locator href="prices.xml#H2O"/> </extendedLink> This is perhaps cleaner, but it's a lot more complicated and not many people (with 2-3 honourable exceptions) seem to be interested in developing XLink applications or software. P. Peter Murray-Rust, Director Virtual School of Molecular Sciences, domestic net connection VSMS http://www.nottingham.ac.uk/vsms, Virtual Hyperglossary http://www.venus.co.uk/vhg 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/ 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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