Mapping ADQL - XQuery

[Tony Linde]

Actually, the subject is more than simply mapping ADQL to XQuery but that is
how it came up (on the subway back from KICH!).

The point really is that we need, in the RI, to specify how identifying an
element in the ADQL WHERE clause that we use for simple searches translates
into identifying the appropriate element in the metadata for a resource. At
the moment, Ray and I can only think of this applying to repeat elements:
i.e., where we have <a><b><c/><c/><c/></a></b>, in the XPath name for
identifying an element we have '[/a/b/c]=99' but which of the c elements are
we checking for having the value 99? Ray implements it as 'any c = 99', but
equally valid is 'all c = 99' or 'first c = 99' etc. 

It is necessary in the RI spec to mandate how this is handled so that the
same query sent to different registries returns the same information. 

1. Personally, I'd vote for 'any c = 99' but let's hear other views.

The second place where this ambiguity occurs is '[/a/b/c]=99 AND
[/a/b/c at x]="Y"' (i.e. 'element c = 99' AND 'attribute x of element c has
value "Y"'): does this mean (if we assume 'any' as the answer to the above
question)
 'any element c = 99' AND 'any attribute x of any element c = "Y"' or
 'any element c = 99' AND 'the attribute x of the same element c = "Y"'

2. I'll pass on this one and defer to the experts.

Bear in mind that whatever we specify as the default, any agent accessing
the registry is free to use the XQuery interface of a registry which
supports that interface to ensure unambiguous querying.

Cheers,
Tony. 
(PS: sorry wiki page not yet updated: cannot get uploads to work from hotel
room!!)

-- 
Tony Linde
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Post:   Department of Physics & Astronomy, University of Leicester
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