Handling semantic heterogeneities using declarative agreements

The focus of this paper is on interoperability issues to achieve data integration in distributed databases for geographic applications. Our concrete application is in the context of the State of Wisconsin Land Information System (WLIS). In WLIS, data is stored in XML using independently maintained local databases. However, answers to many queries must span several databases. Our approach is based on the existence of a central ontology and on declarative transformations, called \it agreements, between the schemas of the local databases and the central ontology. Using our approach, end users can seamlessly query and aggregate semantically related data that is available throughout the state using a visual interface. An expert at the site of the local database uses another visual interface to specify the agreement between that database and the ontology. Our approach has been fully developed and tested.