When you are ranking on number of holdings like OCLC is, a straight
sum makes sense to me---the sum of all libraries holding copies of
any manifestation of the FRBR work is indeed the sum of the holdings
for all the records in the FRBR work set. Of course.
If you're doing relavancy rankings instead though, a straight sum
makes less sense. A relevancy ranking isn't really amenable to being
summed. The sum of the relevancy rankings for various
manifestations/expressions is not probably not a valid indicator of
how relevant the work is to the user, right? And if you did it this
way, it would tend to make the most _voluminous_ work always come out
first as the most 'relevant', which isn't quite right.---This isn't
quite the same problem as OCLC's having the bible come out on
top---since OCLC is ranking by holdings, it's exactly right to have
the bible come out on top, the Bible is indeed surely one of the
(#1?) most held works, so it's quite right for it to be on top. But
the bible isn't always going to be the most relevant result for a
user, just because it's the most voluminous! Summing is going to
mess up your relevancy rankings.
Just using the maximum relevancy ranking from the work set seems
acceptable to me--the work's relevancy to the user is indicated by
the most relevant manifestation in the set. There might be a better
way to do it (Is a work with four manifestations with a relevancy
ranking .7 more relevant than a work with just one manifestation with
a ranking of .9? I don't think it probably is, actually; I think
just taking the maximum should work fine. But it depends on the
relevancy algorithm maybe.). I don't think I'm enough of a
mathematician to understand the point of the log of the sum, though,
At 2:38 PM -0400 4/10/06, Hickey,Thom wrote:
>We're doing straight sums of the holdings of all the manifestations in
>the work. It's hard for me to see the need to discount holdings in
>multiple manifestations. It does mean that 'bible' tends to come to the
>top for many searches, but that's about the only work-set I see coming
>up unexpectedly to the top.
>If we had circulation data we'd certainly factor that in (or maybe just
>use it if it was comprehensive enough).
>From: Code for Libraries [mailto:[log in to unmask]] On Behalf Of
>Sent: Monday, April 10, 2006 2:04 PM
>To: [log in to unmask]
>Subject: Re: [CODE4LIB] Question re: ranking and FRBR
>Thanks...is it just a straight sum, Thom?
>>Here at OCLC we're ranking based on the holdings of all the records in
>>the retrieved work set. Seems to work pretty well.
>>From: Code for Libraries [mailto:[log in to unmask]] On Behalf Of
>>Sent: Monday, April 10, 2006 1:06 PM
>>To: [log in to unmask]
>>Subject: [CODE4LIB] Question re: ranking and FRBR
>>Here's a question for anyone who has been thinking about or working
>>FRBR for creating record groupings for display. (Perhaps others have
>>already discussed or addressed this...in which case I'd be happy to
>>a pointer to resources that are already out there.)
>>In a retrieval environment that presents ranked results (ranked by
>>record content, optionally boosted by circulation and/or holdings), how
>>could/should FRBR-like record groupings be factored into ranking?
>>Several approaches have been discussed here:
>> - Rank the results using the score from the highest-scoring record in
>> - Use the sum of scores of documents in a group (this seems to me to
>>place too much weight on the group)
>> - Use the log of the sum of the scores of documents in a group
>>I'd be very interested in knowing whether others have already been
>>thinking about this....