Emergent Semantics Systems

                                  Karl Aberer

                School Of Computer and Communication Sciences
                             EPFL – Switzerland
                            karl.aberer@epfl.ch


Abstract
Until recently, most data interoperability techniques involved central compo-
nents, e.g., global schemas or ontologies, to overcome semantic heterogeneity
for enabling transparent access to heterogeneous data sources. Today, however,
with the democratization of tools facilitating knowledge elicitation in machine-
processable formats, one cannot rely on global, centralized schemas anymore as
knowledge creation and consumption are getting more and more dynamic and
decentralized. Peer Data Management Systems (PDMS) implementing semantic
overlay networks are a good example of this new breed of systems eliminating
the central semantic component and replacing it through decentralized processes
of local schema alignment and query processing. As a result semantic interoper-
ability becomes an emergent property of the system.
    In this talk we provide examples of both structural and dynamic aspects of
such emergent semantics systems based on semantic overlay networks. ¿From the
structural perspective we can show that the typical properties of self-organizing
networks also appear in semantic overlay networks. They form directed, scale-
free graphs. We present both analytical models for characterizing those graphs
and empirical results providing insight on their quantitative properties. Then we
present semantic gossiping, a model for the dynamic reorganization of semantic
overlay networks resulting from information propagation through the network
and local realignment of semantic relationships. The techniques we apply in that
context are based on belief propagation, a distributed probabilistic reasoning
technique frequently encountered in self-organizing systems. Finally we will give
a quick glance on how this techniques can be implemented at the systems level,
based on a peer-to-peer systems approach.

Biographical Sketch
Karl Aberer is a Professor for Distributed Information Systems at EPFL Lau-
sanne, Switzerland, and director of the Swiss National Centre for Mobile In-
formation and Communication Systems (NCCR-MICS). His research interests
are on decentralization and self-organization in information systems with ap-
plications in peer-to-peer search, overlay networks, trust management and mo-
bile and sensor networks. Before joining EPFL in 2000 he was leading the re-
search division of open adaptive information systems at the Integrated Publi-
cation and Information Systems Institute (IPSI) of GMD in Germany, which
he joined in 1992. There his work concentrated on XML data management and
cross-organizational workflows. He studied mathematics at ETH Zrich where he
also completed his Ph.D. in theoretical computer science in 1991. From 1991 to
1992 he was postdoctoral fellow at the International Computer Science Institute
(ICSI) at the University of California, Berkeley. He is member of several journal
editorial boards, including VLDB Journal, and conference steering committees.
Recently he served as PC co-chair of ICDE 2005, MDM 2006 and ISWC 2007.