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At 12:02 PM 5/12/2002 -0400, Mike Champion wrote:
>"One of the great strengths of XML is its flexibility in representing
>many different kinds of information from diverse sources. To exploit
>this flexibility, an XML query language must provide features for
>retrieving and interpreting information from these diverse sources."
>
>"It is designed to be a small, easily implementable language in which
>queries are concise and easily understood. It is also flexible enough
>to query a broad spectrum of XML information sources, including both
>databases and documents. ... XQuery is derived from an XML query
>language called Quilt [Quilt], which in turn borrowed features from
>several other languages, including XPath 1.0 [XPath 1.0], XQL [XQL],
>XML-QL [XML-QL], SQL [SQL], and OQL [ODMG]."
>
>Maybe "unification of approaches" is too strong, but clearly the
>objective is to query XML views of data irrespective of whether the
>physical data are in documents, SQL databases, OO repositories, or
>native XML databases.
Yes, very much so.
> > I must say that if that is indeed
> > the goal, then it is doomed to failure. RDBMS, OO, and XML are three
> > very different models and I don't think you can usefully combine
> > them.
>
>Well, XML is a universal data meta-format; you can represent SQL, OO,
>and documentL data in XML, and XQuery lets you query that
>representation.
>I didn't mean to imply that XQuery would let you unify the underlying
>data models. It's true that you lose some of the relational model in
>an XML representation (the order of "rows" and "columns" becomes
>significant, and duplicates become allowed all of a sudden, and XQuery
>has to bend over backwards to allow these XML-isms to be ignored, as
>best I understand it).
Right. XQuery does not use the SQL model or the OO model, it relies solely
on the XPath data model. Many aspects of the original sources are lost.
>I personally find this the most appealing aspect of XQuery -- I *want*
>to be able to do a join across an XML document collection and a table
>in an RDBMS, and maybe some topic map or RDF metadata thrown in for
>good measure.
This is one of the main reasons for XQuery, IMHO.
Jonathan
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