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- From: Joe Lapp <jlapp@webmethods.com>
- To: xml-dev@ic.ac.uk
- Date: Mon, 29 Nov 1999 19:59:57 -0500
At 03:22 PM 11/29/1999 -0800, Paul Tchistopolskii wrote:
>[...]
>To me the most critical thing in streaming XML processing
>is do we allow 'look-forward' rules or all of our rules are
>'look-backward'. ( Yacc ). [...]
Yes, in terms of the events that XML parser APIs (eg. SAX) spit out, this requires additional "look-ahead" (at future events) to get the same data. Yes, this will add some complexity to a solution that might otherwise have avoided such look-ahead.
But attributes do not prevent the requirement to do look-ahead. My stream might be filtered on structured data, which attributes never represent. Or it might be filtered on unstructured data which happened to be represented in element content.
The "look-ahead" that you already needed for non-attribute data solves your problem. It does not require anything DOM-like. A stateful SAX-based parse will work just fine.
>I would better not to support look-forward rules at all in
>the core API. If there would be another layer, doing such a
>magic - why not?
You still need this 'magic' in a stateful SAX parse to filter on non-attribute data.
My main attribute issues remain:
- Users want to use attributes to make documents easier to read.
- XML namespaces use attributes for namespace declarations.
And on the flip side:
- Treating attribute values and element content uniformly in layered technologies has caused me and continues to cause me quite a few headaches. But I've argued that this is only because attributes were given semantic distinctions over element content, whereas I think they should have been just a syntactic shorthand for data that would also be valid in element content.
--
Joe Lapp (Looking for some good people to help design
Senior Engineer and build the Internet's business-to-business
webMethods, Inc. XML infrastructure. We are 100% Java.)
jlapp@webMethods.com http://www.webMethods.com
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