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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: RE: XML=WAP? And DOA?
 1/14/2002 2:08:03 PM, Nicolas LEHUEN <nicolas.lehuen@u...> wrote: I wouldn't diagree on the "self describing" bit; tags are just labels that have to refer to something else that defines their semantics. My point vis a vis CSV was simply that a tag is a lot better than nothing (or a header somewhere far away) when you're debugging. > Any given XML document requires a schema, and not only for > validation....an XML application has to rely on an implicit > or explicit schema to process XML documents meaningfully, > i.e. at the semantic level, because it is the schema that > creates the document semantics. > > Well-formedness alone is a lure ... If you don't write the > schema explicitely, its ghost will appear in your programs > anyway, created by the assumption the program has to make > to run properly. THIS is the kind of thing I had in mind when I referred to us talking past each other on xml-dev <grin> http://lists.xml.org/archives/xml-dev/200201/msg00676.html I guess I disagree about the *general* applicability of the situation that Nicolas Lehuen describes. Simon put it quite nicely (emphasis and parenthetical notes added) : "...accept that information may not *always* come in precisely the same structure. [when it doesn't] Write code which supports flexibility rather than demanding conformity. [you can] Throw away notions of strict conformance to semantical notions - rely only on syntactical conformance." In a loosely coupled application you may know very little about the data other than it is well-formed XML, and the job of an application component is to extract whatever information APPEARS to match the patterns it is looking for, put the information in a more useable form, and pass it down the pipeline for further processing. A network of these simple components can do some quite interesting things, and tools such as Sean McGrath's XPipe stuff and Software AG's EntireX Orchestrator are becoming available to develop them. This is a very different way of looking at XML (and data processing for that matter) than the object-centric or schema-centric approach. It solves one problem -- the lack of authoritative schema for many application domains -- by accepting a lot more chaos and error than many might find tolerable. In any real system, there would have to be humans involved to make sure that that purchase order that looks like the deal of a lifetime is indeed what the pattern matcher thought it was and not a joke, a fraud, or something else entirely. But at least they won't reject the purchase order of a lifetime because it had an extra <p> tag somewhere. <grin, yeah I know this is a contrived example!> More seriously, this is a way to exploit what order there is in the system, i.e., an <invoice> tag probably refers to something resembling an "invoice", without insisting on total conformity. This is not to say that this "loose" approach is the best; it's certainly not when you CAN authoritatively specify fixed schemas and reject messages/documents that don't match them. But it's better than handwringing about how XML can only be used once everyone agrees on a schema for some particular industry, as we see so often in the trade press. 
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