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RE: Parallel execution: functions, XPath, XQuery,

From: Michael Kay <mhkay@iclway.co.uk>
Date: Tue, 22 May 2001 05:57:36 -0400 (EDT)
To: "'Ken North'" <ken_north@compuserve.com>, <xml-dev@lists.xml.org>, "'W3C Query Comments'" <www-xml-query-comments@w3.org>, "'XPath Comments'" <www-xpath-comments@w3.org>
Message-ID: <001501c0e2a5$ffeb0f10$664d3c3e@PCUKMKA>
> So issue 1 is how to partition document collections for
> optimal parallel
> execution with XPath and XQuery. I've not found any published
> research on
> parallel evaluation or parallel execution with XPath. Anyone
> have a URL?

There is very little published information on XPath implementation and
optimization at all, let alone parallel execution. But there is nothing in
the language to preclude it - or do you think otherwise?

> 2. The XPath 2.0 requirements document identifies the need
> for additional
> string and aggregate functions, but doesn't define a
> requirement for being
> able to invoke user-defined functions (UDFs). XQuery supports
> XPath functions but it also supports UDFs. A future version
> will support UDFs implemented in programming languages.

XPath 1.0 can already invoke user-defined functions. What it can't do is to
define them. The XSLT 1.1 working draft provides specifications allowing
XPath to call user-written functions in Java or JavaScript. There's a
requirement in the XSLT 2.0 specification to allow external functions
written in XSLT, and there's a similar facility in XQuery.
> 3. If you are using an SQL products such as Oracle 8i and IBM
> DB2, you can
> add UDFs for processing XML data by implementing them in
> Java, C/C++ and
> deploying them as a database plug-in.

> So issue 3 is how to express to XPath or XQuery details such
> as whether to
> use a single instance of the Java class per query or allow
> parallel use of an UDF.
Have you read the XSLT 1.1 working draft? If you think the binding to Java
(for example) could be improved in this area, specific suggestions are
welcome. Certainly, the problem of handling external functions with
side-effects is one that it doesn't yet attampt to tackle.

Mike Kay
Received on Wednesday, 23 May 2001 10:29:09 UTC

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