Re: Call for unifying and clarifying XML 1.0, DOM, XPATH, and XML Infose
> So I see several reasons for the general failure to understand what > groves are all about: > > - lack of suitable presentational material > - the fact that it comes from a different community with a different > philosophy and terminology > - the extreme suspicion with which many W3C (and other) people view > anything coming out of the ISO processes (this is not directed at > you, Michael; I have no idea what your stance is) > - the fact that groves and the DOM have different purposes > Or maybe that groves are just too abstract? (I'm saying this solely based on what I read in the excellent tutorial by Paul Prescod that you referred to.) In fact, even the XML quintessence, trees, is not a clear sell: recursion and trees are a standard part of a computer science curriculum, but these concepts are not easily swallowed by all. The best hope we have is to base what we develop directly on concepts that we can assume have been somewhat understood through training or mathematical intuition. Groves appear well thought-out for their purpose, but the mathematical abstractions they embody are not necessarily any easier to grasp than if those abstractions were applied directly to the problem domain at hand. In fact, it is my experience that formal methods frameworks are often a hindrance to exposing simple ideas. Talking mathematically is not bad, but the talking must be in mathematics that's known: sets, maps, trees, etc, not in a little-known lingo that requires extra training. (By the way, I realize belatedly that Infosets are more or less couched in grove langauge, mostly unknown to the world, whether justified or not. XML Schema is in turn couched in Infoset speak, and so on,....) I am not qualified to comment on SGML itself, but even XML 1.0 does appear to be suffering from over-conceptualization (too many concepts that don't fit together too precisely). As a simple example, look at content models: - a content model is not a model for content in general, but only two kinds of content, namely elements and character data, not processing instructions and not comments (incidentally, it could have been termed "markup model" as well I think, since markup is a more general concept than content) - the content model concept is further split into two concepts: (1) element content, which allows only elements in content (2) mixed content, which allows character data interspersed with elements Thus, there are now two similar sets of syntax and regular expressions for describing not content, but the projection of content onto elements and character data. An alternative approach would have declared "content" to simply consist of just element nodes and text nodes ("text nodes" as in XPATH) representing character data. Then there would be no need for (2), since a content model now describes a regular language over the alphabet consisting of what you would expect: element names and the token text() (or #PCDATA). And, you'd be able to describe, say, HTML with Appendix elements that must appear at the end: ((#PCDATA | H1 | H2 |...)*, Appendix*) So, the distinction between element content and mixed content is a needless one that both restricts what can be expressed and that muddles the conceptual framework. (The way of treating content just outlined is what we chose for the DSD schema notation, incidentally.) XPATH with its tree model goes a far way in clearing up things; so does DOM2, but the crown unifying these not-quite-compatible models is missing. /Nils 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/ or CD-ROM/ISBN 981-02-3594-1 Unsubscribe by posting to majordom@i... the message unsubscribe xml-dev (or) unsubscribe xml-dev your-subscribed-email@your-subscribed-address Please note: New list subscriptions now closed in preparation for transfer to OASIS.
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