[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: Syntax and Semantics
At 03:01 PM 5/18/00 -0700, Marc.McDonald@D... wrote: >I think the cases of actually processing the infornation in a document and >documents from different sources are often overlooked. > > >For example, a document with some MathML, ChemML, and HTML mixed together. A >DTD or schema may allow the syntax of the sections to be validated, but it >won't render the formula, molecule or text. The rendering is done by an >application which understands the semantics of the language involved. > >There is no current specification for the cooperation of rendering engines >for MathML, ChemML and HTML - except perhaps through browser plugins and a >delegating XML browser. > >All namespaces provide is avoidance of ambiguity. All tying a namespace to a >schema adds is validity checking. This states my problem precisely. I need a means of attaching semantics to a document so that people receiving that document know how to process it. The success o browser plugins (despite their drawbacks) mean that the community at large (the 99.99% of web users who haven't even heard of XML) will expect us to solve it transparently, *in a short period of time*. It *is* solved - in large part - for documents carrying single MIME types. I and Henry Rzepa are in the process of mounting a number of *.SVG documents on our web site. They can be used by someone who has never heard of SVG. A user clicks on the link and is sent a document with MIME type image/svg. The browser hasn't heard of this, but asks if I want a plug-in and then goes to try to find it. I don't know where it gets it from, but it manages it. Therefore "*.svg" and "image/svg" both carry effective semantics today. In contrast "http://www.w3.org/TR/someVersion/SVG/SVG.dtd" does not carry any semantics and many XML-DEVers are arguing that it shouldn't. The MIME strategy works pretty well, even outside the formal mechanisms of the IETF. ca. 4 years ago Henry and I wished to use MIME for stamping files with molecules in. We proposed a top-level type of "chemical/" to the IETF - lots of fun discussion for 6 months - and it didn't make it. BUT there is a de facto convention for "chemical/x-*)(enshrined in the formal publication of the International Union of Pure and Applied Chemistry"). It became adopted very quickly. All the chemical sites and most software suppliers use it. If anyone receives a file with "chemical/x-pdb" MIME type, the browser will go out and retrieve a plugin. All this without any official registration of the type. For many pragmatists, this is how the Web actually works. Theoretically broken but extremely useful. It's a 99% solution. There are lots of things "wrong" with this approach, of course: - chemical/x-pdb is not guaranteed to be unique (its not registered). It could be spoofed. - it does not label a resource. If the "PDB" specification changes (which it does, fairly frequently !) the software can break on new files. But it breaks anyway. - horizontal vendors (e.g. browser m'facturers) tend not to support discipline-dependent MIME types. BUT it works for us. We accept all these failings. What pragmatic XML users will not accept is being told that there is no way of carrying semantics for XML files. Or wait 3 years while the name/use/mention/id/resource/label problems are sorted out. The immediate problem is the multiDTD file. We cannot use a single scalar wrapper to describe the semantics. CML documents will contain CML intimately mixed with SVG, MathML, XHTML, CALS/OASIS and 1-2 other common technical DTDs. There either has to be a new wrapper specifying this or there has to be semantics in the file. Either of these require the browser-writers to agree on a common convention. I suggest we decide on such a convention as quickly as possible and promote it. A possible solution could involve PIs. [I choose these because most people agree you can do anything you like with them and not upset anyone else - at least that is what the spec says, I think]. PIs are "ignorable semantics"! So the document contains: <?xdev mime="image/svg"?> <?xdev mime="chemical/x-pdb"?> <?xdev mime="text/xml"?> [xdev represents XML-DEV, but I don't think we can use "xml-dev", can we?] Then purists can ignore these. People who want to use this can do so. The enthusiasts will see how far it goes before it breaks. Meanwhile we shall have developed a more robust semantic/ontological/semiotic approach which can be implemented as the next phase. P. *************************************************************************** This is xml-dev, the mailing list for XML developers. To unsubscribe, mailto:majordomo@x...&BODY=unsubscribe%20xml-dev List archives are available at http://xml.org/archives/xml-dev/ ***************************************************************************
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