SEMANTIC MEDIATION SERVICES IN GEOLOGIC DATA INTEGRATION: A CASE STUDY FROM THE GEON GRID

Semantic mediation services are a means to help integrate disparate data sources. Currently, there are many data sets in the community that are isolated and are not used to their utmost potential. Even though certain data sets are easily accessible, integrating and using them in a research environment is not practical. This is primarily due to the fact that each data provider uses his/her own standards and formats. To alleviate such problems, in the GEON project we are developing an interoperability framework and system that allows a data provider to register a data set with one or more "mediation ontologies" -- i.e. standards for data structure and content -- and subsequently query the different data sets in a uniform fashion. Our test case includes integration of different state level geologic maps. Within the system a user registers a geologic map using interactive tools against previously defined geologic age and rock type classification ontologies. The means to query the mediated data sets is significantly improved when all available data sets are registered in this way: Heterogeneous source vocabularies are made compatible via the ontologies, and multiple conceptual dimensions become queryable simultaneously (e.g., "for all selected data sets, find regions with igneous rocks from geologic period P having composition C, fabric F, and texture T"). In order to answer such semantic queries against the mediated data sets, our system "reasons" with the ontologies and builds the distributed query plans accordingly. The system is embedded in the GEON grid environment, i.e., it both uses GEON grid services (e.g., for remote data access), as well as provides new semantic mediation services for the GEON-Grid (e.g., ontology-enhanced query planning).