>Currently it is not easy with SRU/W to broadcast the same query to many
>SRU/W servers because one has to take into account all the differences
>between different servers.
>

>> Definitely true - this due to the fact that SRW is a client-server
protocol, whereas metasearch broadcasting as you are describing is more
a grid computing task.

One wonders if such problems of semantic interoperability between
server-side implementations are an invariant of the distributed
computing model underlying SRW/SRU rather than the protocol itself,
Z39.50 and indeed any other implementation of that model.
In particular, one wonders whether is the very requirement that servers
align their interpretation of service provision (here searching) that
introduces assumptions about the autonomy of participating parties which
cannot be advanced in a large-scale federated environment.
In this sense, harvesting as implemented in OAI-PMH relieves servers
from any other semantic alignment beyond metadata format and thus suffer
considerably less from these problems. With distributed computing, and
thus with SRW/SRU, each party which contributes its data must also
participate of service provision and this amplifies requirements of
mutual consistency and the problems these requirements raise in a
loosely-coupled environment.

regards,

fabio simeoni

***************************************
Fabio Simeoni
Senior Research Fellow
Centre for Digital Library Research (CDLR)
Computer and Information Sciences Department
University of Strathclyde
Tel:0044-(0)141-5485855