Peer-to-Peer Semantic Integration

                                  Guido Vetere1
                                    1 IBM Italy,

                      Via Sciangai 53, 00144 Rome, Italy
                           gvetere@it.ibm.com



Abstract. Peer-to-Peer computing (P2P) is a model in which each system acts
potentially as both client and server, and systems link the one another without
resorting on centralized services. Thanks to its generality, flexibility, and scal-
ability, P2P is one of the prominent models in the Web. Endpoint-based Web
Services infrastructures, for instance, reflect a P2P nature. Popular P2P sys-
tems are generally limited to the management of simple objects whose descrip-
tion is based on few facets directly encoded in the objects' identifier. This in-
hibits the development of systems that require data to be described by complex
semantic characterizations. Advanced data oriented P2P integration systems
have been recently proposed to overcome these limitations, mostly based on
Semantic Web standards and shared ontologies. As the complexity of the uni-
verse of discourse grows, however, P2P models raise a number of non trivial is-
sues. The notion of? sharing an ontology? in 'loosely coupled' environments,
for instance, should be carefully considered in the light of the basic observation
that the actual interpretation of ontology predicates (i.e. the semantics) dwells
in the shadow of providers? implementation. Moreover, there are contexts in
which global conceptual models are not given at all, and the integration logics
results in a Web of P2P conceptual mappings. Issues like these lead to the need
of giving P2P information integration a suitable formal semantics. We will see
how the classic data integration approach that consists in creating a unique da-
tabase out of a set of information sources turns out to be quite inadequate.
Then, we will present the general idea of an epistemic semantics that allows
thinking at P2P integration in terms of knowledge and beliefs of a set of coop-
erative - and yet independent? agents who access a set of possible worlds. Fi-
nally, we will discuss some deep implication of this idea and outline research
directions.