Mike Taylor wrote:

>>Date: Fri, 4 Jun 2004 09:33:17 +0200
>>From: Marc Cromme <[log in to unmask]>
>>
>>What is really needed for federated search and merging of hit sets is:
>>
>>1) an by the appropriate relevance ranking algorithm ordered response
>>set from any of the SRW servers - that's what you are adressing
>>
>>
>
>Yes.
>
>
>
>>2) an indication of the actual relevance value of every record in
>>the hit set (this needs a new SOAP tag in SRW)
>>
>>
>
>No SRW changes are needed for this: there are already two mechanisms
>for including this information.  One is just to add it to the returned
>record, so instead of a DC record you get a DC-with-relevance-score
>record.  The other, which was invented specifically for this kind of
>thing, is an extraRecordData packet (which would need to be requested
>with an extraRequestData packet in the search request.)
>
>
>
Less is more:

approach a) woun't fly, since then I have to know each server
specifically to figure out where in the returned record this information
is buried, and in which form. What a hell of a logic to write for a
federated search over some 30-50 targets!

approach b) is much better, but only  if all agree that the same tag is
used inside the extraRecordData packet to carry this information, and
that all servers agree to encode it in some unified fashion.

I do not have SRW on my fingertips, but I belive that there is no such
'reserved' tag inside the 'extraRecordData' tag, and if it is not
defined by the standard, we are back to the problems of approach a).

>>3) an indication of the possible range of relevance values for each
>>server implementation - I can not meaningful merge ranked hit sets
>>of two servers if the one assigns ranking values [0, 10.000] and the
>>other [-inf, +inf]. So the servers have to tell me in what range
>>relevance values will be.
>>
>>
>
>This is best transferred as an extraResponseData packet.
>
>
>
And also, it's best defined by the SRW standard how the tags are named,
and in which form the data is carried.

>>Obivously, ther must ne made place for 2) and 3) in the  SRW
>>protocol.
>>
>>
>
>Already done :-)
>
>
Not really in a usefull way...

Marc

> _/|_    _______________________________________________________________
>/o ) \/  Mike Taylor  <[log in to unmask]>  http://www.miketaylor.org.uk
>)_v__/\  "Last year I read something by Anita Shreve, but can't
>         remember anything about it at all except that the cover
>         was light blue.  It was the best part of the novel" --
>         Jane MacDonald.
>
>--
>Listen to free demos of soundtrack music for film, TV and radio
>        http://www.pipedreaming.org.uk/soundtrack/
>
>
>