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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] RE: Enlightenment via avoiding the T-word
 > From: Don Park [mailto:donpark@d...] <snip/> > What we need is a XML processing framework that supports > molecules and atoms > design pattern. What we don't need is more complications and fancy > if-but-when-must at what I consider to be lexical slum level. > *argh* I am > starting to sound like Len. I'd go even further. We need an XML processing framework that accepts the plurality of application domains without prejudice or favoritism. We need an XML processing framework that does not take a specific metadata vocabulary for annotating information items and a particular set of transformations and bless them and insist that everyone accept the notion that these are not annotations and transformations, but rather the process of realizing an XML instance's True Form. The only true form of an instance is that of the instance itself, and that's nothing but a bunch of text and pointy brackets. Everything else is layered atop that to suit a particular application domain or processing model. I'll put forth a different formulation of some thinking I tried to express yesterday. I feel like I've had an epiphany (though that feeling may evaporate once someone rhetorically rips me to shreds). It is very typical for an XML application to want to associate certain metadata with XML information items to suit certain processing needs. One can easily envision different metadata vocabularies to suit different domains. None of these are inherent in the instance itself. None of the processing done with the instance and associated metadata is a realization of the instance's true form. The only true form of the document is that which is in the instance itself, and that's just a bunch of text and pointy brackets. One particular class of application is that which we call a validator. The metadata a validator wishes to associate with an information item is a grammar or set of rules that express a set of constraints. Validators verify that a document satisfies the collective set of constraints associated with its information items. If the document satisfies the constraints, the validator passes it on to another application for further processing; otherwise, the document is rejected. There is no such thing as well-formed but inherently invalid XML document. It is only invalid within the context of a particular domain, and the constraints suited to that domain can be expressed in a schema. Another class of application is transformers. These produce a different information set better suited for processing within a particular application domain. At one extreme, we have those that associate XSLT templates with elements, and use these to transform a document into something potentially quite different. At another extreme we have those that do very simple transformations, such as adding default attributes. Then there are many shades of gray between these extremes, such as Simon's namespace-mapping SAX filters. There is no such thing as a wrong transformation, except one that produces an unintended result. Other applications may wish to annotate information items with additional labels that provide hints to applications for further processing. For instance, one may want to attach a label to elements "shippingAddress" and "billingAddress" that indicate both of these represent addresses and should be processed as such by an application. We should not be enshrining one metadata vocabulary in a PSVI and insisting that that one vocabulary and no other is intrinsic to the true form of document instances. With the status quo, however, validators are accorded special status. They are not like other applications. The processing they do is regarded as something very fundamental and inviolate. In addition, validators are allowed to add certain annotations from a specific blessed metadata vocabulary (XML Schema), and they are allowed to perform certain specific blessed transformations. These blessed transformations and annotations are considered part of the true form of the instance, enshrined in the PSVI, and annotations or transformations that are not blessed are derided as desecrations of the infoset. The lines drawn strike me as rather arbitrary. If we reject the PSVI, and if we accept there are no wrong transformations (except those that produce an unintended result), and if we accept that there are potentially many metadata vocabularies suited to different application domains and many valid processing models, and that none of these are somehow intrinsic to a document instance, then it seems to me that much of the fodder for argument simply evaporates. One can even imagine a more flexible schema mechanism that can be invoked in different modes like an XSLT stylesheet. One could invoke it in "elementFormQualified" mode, or "elementFormUnqualified" mode; the application gets the information in the form most suited to its needs, and we dispense with religious debate over which is its true form. In hindsight, now, I have to agree with Mike Champion's post about scholasticism[1]. This debate smacks of scholasticism because it centers so much on the debate about the true form of an XML instance. I think the XML world needs its renaissance, and we must start by dethroning the PSVI. [1] http://lists.xml.org/archives/xml-dev/200108/msg01020.html 
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