[Q] Xalan 2 and Serial XPath

[Andy Clark <an...@apache.org>]

I just joined the mailing list for Xalan because I'm looking into
implementing unique/key/keyref Schema functionality in Xerces.
Because you specify the selector and field elements using XPath,
I figured that this would be the perfect place to look for help.

The problem is that we don't want to buffer the entire tree in
order to apply the XPath expressions and match the selector and
fields. This is a *major* performance problem! 

Anyway, we're going to suggest that the Schema working group 
limit the power of XPath allowed in Schema to those that can be 
processed in a serial manner. This being said, I would like to
know if there is any plan to support this type of functionality
in Xalan 2. And besides not supporting look-ahead, look-aside,
etc., is there a way to drive the matching based on the 
callbacks from the parser?

I'm starting to look at modelling this type of behavior and
came up with a simple interface for document segments. Since
selectors and fields are only "active" within a specific
scope, I thought that it would be a good idea to have an
XPath matcher be driven by these callbacks and provide some
simple mechanism for when a match occurred.

I quickly read over the Xalan 2 design document and skimmed
the JavaDoc so I'm sure I missed a lot. So I'd appreciate it
if someone could tell me if this is possible in Xalan 2 *and*
if there is a way where we can pull this functionality into
Xerces without bringing the entire Xalan implementation.

-- 
Andy Clark * IBM, JTC - Silicon Valley * andyc@apache.org