* Summary:

In order to retrieve only the elements that are actually wanted for
display it is proposed that an 'recordXPath' parameter is added to the
searchRetrieveRequest message.  This would contain an XPath expression
dependant on the recordSchema parameter to be applied to the records
before returning them.

* Background:

SRW/SRU can be used to retrieve XML records of any size or schema,
including such things as TEI, EAD, SVG or X3D which are often extremely
long and/or complex.  A client cannot ask for sections of a record, so
must currently either request the entire record and throw unwanted
sections away, or rely on the server to provide a set of appropriate
schemas to retrieve the sections. In particular, a simple 'title list'
display is frequently used, but often have different fields displayed
depending on the target audience.


* Changes to searchRetrieveRequest:

A new, optional, string parameter called recordXPath.  It would come
immediately after recordSchema in the XML.  It would contain any valid
XPath expression, though the server may choose to reject it.


* Changes to searchRetrieveResponse:

No protocol changes, however clients must be aware that if a multipath
expression is requested, then the recordData returned may have multiple
top level tags.

For example:
    <recordXPath>/record/title|/record/creator|/record/date</recordXPath>
would generate:
    <recordData>
      <title> ...
      <creator> ...
      <date> ...
    </recordData>

* New Diagnostics (to be assigned numbers):

XPath retrieval unsupported.
XPath retrieval not authorised.
XPath retrieval expression invalid.
XPath retrieval expression invalid for requested schema.
XPath retrieval expression invalid for this record.
XPath retrieval expression contains unsupported feature(s).


* Related Proposals:
To add a unique record identifier to the diagnostic schema to allow
for retrieval of records represented by surrogate diagnostics.


Rob

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