(Please excuse the cross-postings.)

While I am tooting my own horn here, and recording it in mailing list
archives for posterity, the folks at Ariadne have published an article
I wrote called "An Introduction to the Search/Retrieve URL Service
(SRU)". From the article:

   This article is an introduction to the "brother and
   sister" Web Service protocols named Search/Retrieve Web
   Service (SRW) and Search/Retrieve URL Service (SRU) with
   an emphasis on the later. More specifically, the article
   outlines the problems SRW/U are intended to solve, the
   similarities and differences between SRW and SRU, the
   complimentary nature of the protocols with OAI-PMH, and
   how SRU is being employed in a sponsored NSF (National
   Science Foundation) grant called OCKHAM to facilitate an
   alerting service. The article is seasoned with a bit of
   XML and Perl code to illustrate the points. If index
   providers were to expose their services via SRW and/or
   SRU, then the content of the 'hidden Web' would become
   more accessible and there would be less of a need to
   constantly re-invent the interfaces to these indexes.

I think these Web Service protocols, SRW/U, hold A LOT of promise for
searching the "hidden Web". I think it behooves us folks in Library
Land to implement these protocols against locally developed,
Internet-accessible indexes. Since the stuff returned from queries
against SRW/U implementations are pure XML it is much easier to reuse
this stuff for many and varied purposes. Display. Storage. Syndication.
Meta searching. Etc.

"Just give me the data!"

Eric Lease Morgan
University Libraries of Notre Dame