[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: XML Information Set Requirements, W3C Note 18-February-1999
Paul Prescod wrote: | I don't believe that the W3C has forgotten about stream processing. One of | the more controversial parts of the XML namespace specification is | intimately tied to stream processing (local namespaces). I think that I | can safely say that when XML was being developed streaming uses were as | high in the minds of the working group as tree-based uses. Stream based | processing has always been more common in the SGML world than tree | processing. Okay then, why are the DOM and XSL tree based? Well, the web | infrastructure favors small documents inherently. Large streams must be | broken up on the server side for performance reasons. Bandwidth, not RAM, | is the limiting factor in Web user interfaces. This clears a great deal up for me. Thank you. I didn't see the direct relationship between usage of XML for stream processing and local name spaces. Thus, a similar controversy would arise if one proposed local architectures? *evil grin* Jeff Sussna write: | If you approach XML as a type system, the concept of document loses | its first-class status (or at least should, in my opinion). <warning up-time="34h"> I think I agree with this. Please correct me, but with Property Sets, each node has a link directly to the 'document root'. I see this as something which deserves consideration (among other things) when the Infomation Set is defined. Perhaps it can look like this: BaseInfoSetItem { // stuff common to both stream and object representations } TreeInfoSetNode public BaseInfoSetItem { // extra stuff that you get for free when the representation // is an in-memory graph, database wrapper, or some other // complete object with random access. TreeInfoSetNode *DocumentRoot(); } EventInfoSetStack public BaseInfoSetItem { // extra stuff relevant when you have an event based, stack // representation of the information in question. This would // be the same as the 'visitor' interface for the TreeInfoSet? } </warning> Hmm. Just meandering... Rick Jelliffe replied to Jeff's note: | XML is not a type system. A document is a graph of elements, data, | comments and PIs with | * an ID namespace | * optionally some element type declarations | * optionally some entity declarations and notation declarations | * optionally namespace declarations which allow local type names to | be qualified by a URI | | In other words, the document is the block mechanism for metadata | and namespaces for a subtree of the entire hyper-document. Hmm. Perhaps this would be a good starting place for the 'definition' of a document. Thus, would it be fair to say that a document is analogous to a database transaction? If so, then my question becomes: How can I express nested blocks? | XML is a labelling notation, not a type system. I'm not sure I get the distinction. When you label something arn't you in effect classifying it, i.e., giving it a type, and, isn't a label required to identify type? | If the document loses its first-class status, which of these things | should be gotten rid of? Do you want arbitrary scoping of IDs, element | type declarations, entity declarations, notation declarations and | namespaces? If so, you need some block mechanism to allow these. Hmm. Well, I see a stream based system having a stack. Thus, each <tag> beginning something puts the element on the stack, and each </tag> pops the stack. Thus, I see <tag> and </tag> as my block mechanisms. Is this too niave? Don Park wrote: | Why not have "from here on use these declarations" as the | default behavior and then introduce 'push' and 'pop' constructs? | 'push' would save current declaration settings and the 'pop' would | just restore to the saved settings. Mabye I'm not getting it, but <tag> and </tag> provide the push/pop mechanism automagically. The only things that have problems is those "from here on" things. It's unfortunate that SGML backwards compatibility dictate that this is the default behavior... and thus <tag> </tag> can't provide the push/pop mechanism? *dazed* I think I need to go back and do more real-world hacking, I'm starting to get a better felling for XML. Sorry for butting in the conversation again. :) Clark Evans xml-dev: A list for W3C XML Developers. To post, mailto:xml-dev@i... Archived as: http://www.lists.ic.ac.uk/hypermail/xml-dev/ and on CD-ROM/ISBN 981-02-3594-1 To (un)subscribe, mailto:majordomo@i... the following message; (un)subscribe xml-dev To subscribe to the digests, mailto:majordomo@i... the following message; subscribe xml-dev-digest List coordinator, Henry Rzepa (mailto:rzepa@i...)
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