Fw: [SML] Streaming XML processing. ( Whether to support Attribute or not? )

Joe Lapp jlapp at webmethods.com
Tue Nov 30 00:56:58 GMT 1999

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 at webMethods.com           http://www.webMethods.com

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