Cart
|
[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: Data Model(s) for XML 1.0 / XML Devcon / DOM / XSL / Query
 Robin Cover wrote: > Hmmm... You wrote: > > > By permitting an instance document to stand on > > its own as syntax, without the expected pre-ordained > > semantics expressed in a DTD.. XML took the decisive > > step which SGML never had > > I don't understand, unless something is lurking in "expected" and/or in > "pre-ordained". What is lurking is the 'pre' in "pre-ordained" (which implies 'expected'). If nothing is expected, then it is legitimate to consider only the body of the instance document. If a content model or schema is desirable as a means to describe the document structurally, generically, or abstractly, then it can be derived from the instance. The traditional rationale for validation is to insure that the document as received corresponds to the document type expected, as expressed by its DTD, and there are plenty of cases where it is appropriate to examine an instance on that premise. My more radical view is that XML is inherently eXtensible through Markup, rather than by the expansion or relaxation of the content model to accommodate new instance expressions. Embracing well-formedness as the single criterion for accepting an instance document, and in the workaday world thereby being obliged to process it in whatever way your node processes documents of that class, has some surprising consequences for those who expect the traditional logic of validation. Chief among them is that it shifts most questions of whether to accept a document from the parser to a more application specific processor. Having passed basic well-formedness syntax checking, a document or a data structure within that document must be accepted as what it says it is: if the markup says that it describes a <payment>, then it is a <payment> precisely because it says so. The question at that point is whether the particular form, as well as the data content of that <payment>, can be accurately and usefully processed by the existing application software at that node. That is a question which can be answered only at that node, and not in the general or abstract case, but only in light of that instance data. As is the usual case with application software, the answer will depend upon specific error- and sanity-checking routines determining whether that software can render a usable result from that data in that instance environment. In a *slightly* more generalized fashion, this is also what the PSVI is really about: after well-formedness syntax checking, perhaps validation, document or data structure type identification, and then demonstrated data schema conformity, the data is rendered into an infoset which the processing software expects. This is a valid model on which to create application software, but it is not the only one--and often not the most efficient. It does illustrate, though, that the procedure for building application software to a PSVI is just that: a processing model must be determined, unwanted interaction of components must be mediated, etc. The real question is whether we can ever sufficiently (and reliably) generalize the operations of such software, to the point where it can be fed a single generalized post-parse-and-other-preparations data model. I chose to work with XML because it frees me from having to know what the processing, beyond basic well-formedness syntax checking, might be at a remote node--which is just as well because most of the remote nodes with which I exchange data (often indirectly) won't tell me (keeping it secret is their business edge), and some of them don't know who I am, nor that I am the source or a downstream user, of data which they consume or emit. Respectfully, Walter Perry 
|
PURCHASE STYLUS STUDIO ONLINE TODAY!Purchasing Stylus Studio from our online shop is Easy, Secure and Value Priced! 
Download The World's Best XML IDE!Accelerate XML development with our award-winning XML IDE - Download a free trial today! Subscribe in XML format
|
|||||||||
