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At 5:23 PM -0500 1/3/02, Champion, Mike wrote:
>Strong typing - There is a real-world use case for ensuring that queries
>return schema-valid results, for example ensuring that they can be displayed
>in valid XHTML. (Whether anyone outside the W3C cares about schema-valid
>XHTML is another matter, but it is a "real world" example that I'm sure has
>counterparts with more data-oriented schemas in the REAL real world)
I'm interested in hearing more about this requirement. Personally, my
general reaction is that the only thing that should be guaranteed out
of an arbitrary XQuery result is well-formed XML. Any particular
syntax beyond that is a question for the author of the query. By
metaphor with SQL, a SQL SELECT statement produces a table. However,
there's no guarantee that this table has the same schema as any other
table in the database. It may or may not depending on what the SELECT
statement did. I view XQuery similarly.
Suppose I do write an XQuery and I want its output to be valid
according to some schema. If I run the query and it produces invalid
data, then that's a bug in the query, which will likely be detected
by a validation performed in a different, later layer. I will then
fix my code, just as I would for any other bug.
What else would you want XQuery to do? Should it throw an exception
of some kind? Return a default document? Start global thermonuclear
war? What?
I view a query as a function that operates on an arbitrary
well-formed XML document, and which kicks out a defined result for
any well-formed document. If the results don't really make sense for
some inputs, then I'll attach a validation layer to the input
documents before I make the query. If I'm worried about what comes
out of the documents, I'll attach a validation layer after the query
has run to check the output. I'm just unclear on why this needs to be
part of the XQuery layer.
--
+-----------------------+------------------------+-------------------+
| Elliotte Rusty Harold | elharo@metalab.unc.edu | Writer/Programmer |
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| The XML Bible, 2nd Edition (Hungry Minds, 2001) |
| http://www.ibiblio.org/xml/books/bible2/ |
| http://www.amazon.com/exec/obidos/ISBN=0764547607/cafeaulaitA/ |
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