[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] A bit of pedantry (was Personal reply to Edd Dumbill's XML HackArticle.
"Thomas B. Passin" wrote: > In this sense, your semantics may be my syntax. XML markup lets a processor > know how to build a generic tree, or, SAX-like, send certain events. So in a > way the markup functions as a kind of semantics for an xml document, at least > at the level of the lowest level of processing. It appears that there are > layers to this semantics business. Yes, there are layers. One underlying question in this discussion is which of those layers are inherently XML. In my experience of this list, and the community it serves, the extent of general agreement extends only so far as to include well-formed XML markup. Even within the XML 1.0 specification, the question of the canonical semantics of XML is raised by the optional nature of validation. The dividing line seems always to be a process. To elaborate from the syntax of an instance of well-formed XML the additional semantics of validity requires further processing. That such processing is optional under the XML 1.0 specification corroborates the conclusion that the inherent nature of XML syntax extends only so far as well-formedness. That same conclusion also permits e.g. the W3C XML Schema mechanism to substitute different processing than that required for DTD-based validation and, as it outcome, the elaboration of different semantics. The examples you cite of building a generic tree (i.e., W3C DOM and some analogues) or emitting SAX events are other alternative processes which may be invoked to elaborate additional semantics beyond those of simple well-formedness checking. Namespace processing also requires its own processing, which elaborates further semantics. The contentious question is always which of these processes are 'core' or even mandatory to XML or, asked from the opposite perspective, which of them elaborate the expected or canonical semantics of an XML instance. The Infoset offers one, but not the only possible prescriptive to answer that question. In disposition of those instances which do not meet its expectations (as e.g. by invoking no namespace processing) the Infoset declares that they have no infoset, which is probably a reasonable laissez-faire conclusion. The contentious political problem arises when other specifications take the Infoset as their starting point and imply (or more) thereby that its one (out of many possible) semantic elaboration is the baseline definition of XML. In my skepticism about the Infoset I am probably in the minority, but I attempt to reinforce my opinion by always speaking of additional semantics as elaborated from processes beyond what is required for simple well-formedness checking. Because there is no doubt what those processes are, I do not think we should blur the line between syntax and semantics by saying 'your semantics may be my syntax'. You may well regard the processes by which you elaborate your semantics as essential to the nature of XML, but you do not thereby drive those processes onto the common ground which well-formedness occupies, and from which any additional process beyond well-formedness checking loses a significant number of adherents in this community. > I ask again, why are we using markup? From the above viewpoint, the markup > moves a layer of semantics out of the processor and into the document or data > set (of course, doing so in a standard way). I hope that it is now clear why I disagree so strongly with this characterization. The instance document has an integrity which is grounded in its markup syntax and unchanged by whatever processing may be performed, and whatever semantics thereby elaborated. Processing never creates a new baseline in the sense that the document is a syntactic baseline. Yes, we need to pipeline these processes in order to achieve highly specific data handling solutions. Yet the underlying documents remain intact, and in different circumstances, for different purposes, may be submitted to entirely different processes, and yield on each occasion appropriately different semantics. 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
|