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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: RE: Namespaces Best Practice
 > > > > 1) An XML Namespaces best practice for document/application design is > > > > to define all namespace prefix bindings at the document (root) > > > > element context. > > > > For the record: yeech! > > > > In every style guide I've ever seen, the guidance for lexical scoping > > mechanisms is to use them to localize information to its most natural > > scope. Loop-private variables are invisible outside the loop, etc. > > For the record, this best practice is lifted from "Common XML" itself a best > practices guideline: > http://www.simonstl.com/articles/cxmlspec.txt That writeup adopts a per-file definition of "most natural scope", which is more extreme than any definition I'd adopt, though it fits into the "wriggle room" which I mentioned. That's a bit less extreme than what you wrote, though that still wouldn't make me adopt it! :) > I fail to see how a "loop private variable" relates to a namespace defined > by a URI. This is like comparing apples not with oranges but with entire > countries which themselves have farms which themselves contain orange > groves. That's like ... hyperbole! The relationship is: both bind values to names. Both use "lexical scoping" to determine values at use point. > > (The analogy to Java package names is false; that's not a lexical > > scoping mechanism. Block scoped variables are examples of > > lexical scoping mechanisms in Java and most modern languages. > > "xmlns" declarations are lexically scoped.) > > You need to understand this recommendation in its entirety. I do not > advocate reusing namespace prefixes, and so the use of namespaces in order > to accomplish "block" scoping is not really that important (IMHO). Information scoping (one variant is "information hiding") is a classic best-practice in systems development. Lexical scoping isn't only to support rebinding of names to values; it's also to minimize the amount of global state (vs maximizing it, per the CXML policy or the one which you proposed). > I do see > reasons why such lexical scoping may facilitate "cut and paste" operations > on namespace qualified documents, but that is a minor role of namespaces in > XML. Cut'n'paste is a task, not a role, and one which is exemplary of many other tasks. I can understand that you may not care much about those tasks, but that doesn't mean that they're not common parts of working with XML. > We need to see the role of XML Namespaces in a larger context than mere > lexical scoping. Indeed an XML Namespace is very much like a Java package. Maybe you're talking about a policy for what the namespace URI denotes, not about the policy for managing binding of those URIs to prefix names (or as a default prefix). There are other policies; the namepaces spec doesn't touch on any preferred policy. If that's what you're talking about, I claim apples/oranges! :) - Dave 
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