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At 04:46 PM 9/20/99 +0800, James Tauber wrote: >> Meaning one grammar + vocabulary -> language? Where the quantities are all >> one? > >You don't actually need the "vocabulary". The alphabet of a formal language >is part of the grammar. In XML-based languages that rely on DTDs or schemas, yes. But in all formal languages? Seems that it wouldn't be hard to create a formal language that had classes of vocabulary (like noun, verb, adjective) and fit them into patterns (subject[noun]-verb[verb]-object[noun]) that were separate. Hopefully, it wouldn't look like English, but it does seem like a practical solution to a lot of problems. >> I think in practice you may find multiple grammars used within the >> same language, even a formal one > >Ahh. But now you are using "language" in a way other than "the set of >utterances generated by the grammar" right? Unless you mean that sometimes >the same syntactic rules can be expressed two different ways eg > >a+ > >versus > >a a* It's that, but it's also worse. Suppose you have a nice modular DTD that expresses most of the vocabulary a user will need to create documents of a certain type, but has ANY sections so that users can organize it any way they like. Users build sets of DTDs to see what exactly it is they're getting or producing, but all of the possibilities are actually open. Is the language described by the 'master' DTD, which doesn't get you very far? Or is the language described by the particular DTDs? Or do we measure interoperability? A 'master DTD' containing all possibilities will quickly grow obese. Then there's the simpler case of well-formed documents, for which we can _derive_ grammars, but can't make definitive statements above the level of XML 1.0 conformance. >> and (yuck for some) not just subsets (once you let ANY in the door, it all >goes). Trying to keep it all >> exclusively singular seems to be a common dream throughout computing, but >> one I hope we can leave behind more and more over time. > >Let me stress again, I am not saying you can always have a single grammar >for a particular "language". I am saying that you can have a single grammar >for a particular "formal language in the sense used by Paul". I think 'formal language' in that sense is not especially useful except for limited situations, and should probably be reserved for the few cases where XML development is limited to representations of older legacy systems that relied on formal languages based on that sense. XML itself, it seems, can do better than that. >> I think we might do well to ponder whether XML is really about creating >> formal languages or for encoding information already represented in >natural >> languages. If it's the latter, the results might be more interesting. > >Why can't it be both? Isn't that the whole point of write schemata >(including DTDs)? Isn't it about formalising the encoding of this >information. It depends on what kind of 'formalizing' you want to do. In many cases, I'd suggest that we focus on 'relaxing', producing more flexible models that aren't so concerned about locking everything down into a single grammar and a single vocabulary. It requires a change of mindset. Why is it that only one validating Java parser allows the application to continue after a validity constraint (not a well-formedness constraint) has been violated? I suspect it's because a lot of folks are taking the 'formal grammar' of DTDs more seriously than the XML 1.0 spec itself does... [See David Brownell's report on XML.com at http://www.xml.com/pub/1999/09/conformance/summary.html] I don't think we're incompatibly far apart, I just would like folks to look at 'formal languages' a bit more closely and a bit more critically. Rick Jelliffe's made excellent arguments in other postings on this thread, for example, regarding the ways formal languages can obscure as well as illuminate. Right now, I think we need to contemplate whether 'formal grammars' sufficiently distinguish 'languages' in practice before putting extra work for programmers and authors (namespaces) on every formal grammar that comes our way. Simon St.Laurent XML: A Primer (2nd Ed - September) Building XML Applications Inside XML DTDs: Scientific and Technical Sharing Bandwidth / Cookies http://www.simonstl.com 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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