Where can I attend an interesting database workshop close
to a sunny beach? Who are the strongest experts on service
computing based upon their recent publication record and
accepted European projects? Can I spend an April week-
end in a city served by a low-cost direct
flight from Milano
offering a Mahler's symphony? We regard the above queries
as multi-domain queries, i.e., queries that can be answered
by combining knowledge from two or more domains (such
as: seaside locations,
flights, publications, accepted projects,
conference offerings, and so on). This information is avail-
able on the Web, but no general-purpose software system
can accept the above queries nor compute the answer. At
the most, dedicated systems support specific multi-domain
compositions (e.g., Google-local locates information such as
restaurants and hotels upon geographic maps).
This paper presents an overall framework for multi-domain
queries on the Web. We address the following problems: (a)
expressing multi-domain queries with an abstract formalism,
(b) separating the treatment of "search" services within the
model, by highlighting their dierences from "exact" Web
services, (c) explaining how the same query can be mapped
to multiple "query plans", i.e., a well-dened scheduling of
service invocations, possibly in parallel, which complies with
their access limitations and preserves the ranking order in
which search services return results; (d) introducing cross-
domain joins as first-class operation within plans; (e) eval-
uating the query plans against several cost metrics so as to
choose the most promising one for execution. This frame-
work adapts to a variety of application contexts, ranging
from end-user-oriented mash-up scenarios up to complex ap-
plication integration scenarios
