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> Just when we are about it - an xpath expression on CQL ?? Something like
> /this/that[@attribute="xyz"]=somestuff

We can sort of already do this if the CQL parser allows for quoted,
dynamic indexes. Equally, the value could be hacked into a relation
modifier value with a magical index.

foo.magical any/foo.xpath="/this/that[@attribute='xyz']" somestuff

However it does not fit the abstract data model of SRW nor CQL, as we
cannot determine several crucial things required to process the above

*  Schema that the server uses internally, if any
*  Schema that the XPath expression should be applied to
*  Namespaces for the XPath expression

Secondly, XPath over the wire is practically never the right solution.

If you control the server, then you can define an index in a profile which
resolves to that XPath.  If you don't know the data, then you can't tell
what to use in the XPath.  If the data changes, your query is suddenly
inaccurate (eg going from one version of a schema to another) or if the
data is heterogeneous (MODS data and MARCXML data in the same database)

So the only situation in which it would be useful would be:

* The server only supplies one schema, or can determine which schema to
   use from the XPath expression
* The records do not use namespaces
* The client knows the data and the schema
* The data is completely homogeneous

Hence there isn't an official XPath query type.


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