Query Languages for XML

[Joe Lapp]

What query languages are under development for use with XML
documents?  I'm talking about data management query languages
akin to SQL and OQL.  I can envision immense repositories of
highly dynamic content.  It seems to me that such a query
language will eventually become necessary to access or change
XML documents that are shared among many users.  The language
would also need to be a standard to ensure that the clients
and servers of different vendors will interoperate.

Designing a standard that queries a single repository might
be relatively straightforward.  Designing a standard that
allows queries across multiple repositories might be a bit
more of a challenge.  (Think of a future internet in which
documents are related by extended links that assign roles
to everything, and imagine performing a read-only query
across the whole mesh of globally distributed documents.)

I am aware of the SgmlQL and SDQL languages, although I know
only what can be gleaned from an hour's browsing on the web.
(See http://www.lpl.univ-aix.fr/projects/SgmlQL/ for info on
SgmlQL.)  I'd rather see something more object-oriented, like
ODMG's OQL, or something that uses XML to specify queries.

BTW, Microsoft's XML-Data would be quite a boon for such a
large XML repository.  Clients could use XML to specify new
document types or to change existing document types, and
the whole DTD schema could itself reside in the repository.
One query language could be used to maintain both the data
and the DTDs.  If the query language were in XML, it itself
would be extensible.
--
Joe Lapp (Java Apps Developer/Consultant)
Unite for Java! - http://www.javalobby.org
jlapp at acm.org

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