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From Thomas Mahler <thm...@web.de>
Subject Re: XPath/XQuery engine to query OJB
Date Fri, 10 Oct 2003 06:23:07 GMT
Hi Brian,

Sorry for the delayed answer, I was just too busy this week...

Brian McCallister wrote:
> A coworker (my boss actually, hi Terry) was asking the feasibility and 
> LOE I thought would be involved to provide XPath type queries against OJB.
> As I haven't yet tried to build a query engine on top of the PB or OTM 
> layers I thought I would defer that question to the list. I know Matt 
> and I have discussed writing new query engines against the OTM -- can 
> anyone with a better understanding of the ODMG parser, or building 
> parsers backed by Criteria comment?

I was involved in designing the OJB ODMG parser. I've also been involved 
in writing parsers and translators for other query mechanisms like LDAP 
or TopLink Expressions to OJB Criteria.
Against this background I tend to believe that writing an XPath query 
parser won't be difficult.

I have only little experience with XPath, but from what I've seen I 
think that there is a natural match between XPath expressions and OJB 
Criteria objects.

OJB criteria provide a simple AST structure. They are very handy to use 
in parsers and translators.

The only open question is, which parser generator to use. My favourite 
is Antlr, As I have seen several successful projects using it.

Of course having support for additional query languages is a good thing 
for OJB and I'm happy to assist you if you choose to work on this topic.

cu,
Thomas

> 
> Thanks,
> Brian
> 
> 
> 
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