Ontology Alignment for the Semantic Integration of Heterogeneous Geospatial Data Sets

As a growing amount of networked information is becoming available, the potential of a large variety of applications accessing that data in a flexible and transparent way using a single query is far reaching. Particularly important is the case where hundreds of such data sources need to be queried in geospatial, scientific, educational, and e-commerce applications. For example, in homeland security applications, queries on a variety of different domains, e.g., geospatial, biological, and governmental, should be deployed with relatively little effort. A fundamental issue is the integration of data whose schemas display semantic heterogeneities. We have been working on an approach where no a priori integration of all the data schemas involved is needed. Instead, querying can be easily extended to a new data source [3, 5]. Our approach has been used in real-world scenarios in the geospatial domain [1, 4, 6] and leverages current or emerging Semantic Web standards for the storage, interchange, and processing of data. We have adopted an ontology-based interoperation mechanism, whereby a global ontology and the ontologies that describe the distributed data sources need to be aligned so as to establish mappings between the global ontology and each distributed ontology. A homogeneous view over all the data sources is thus obtained [2, 7]. We have investigated ways to help experts establish such mappings using a combination of manual methods, which are needed for the accuracy of the mappings, and automatic methods, which are needed to facilitate the experts’ tasks. Those mappings produce agreements, which are declarative and therefore easy to understand and to maintain. Such agreements are automatically incorporated into the queries that result from the translation of the end user’s query, which is expressed using concepts in the global ontology. The Agreement Maker is a software tool that we have been designing, implementing, and user testing. It is used to create the mappings between the global ontology and each distributed ontology and to generate an agreement document. Figure 1 shows a user interface that is part of the Agreement Maker. The two hierarchies that represent the ontologies are displayed in two separate panes. The expert browses through the contents of the ontologies and establishes the mappings between each concept (or group of concepts) in the global ontology and the corresponding concept (or concepts) in the distributed ontology. A deduction module is integrated into the Agreement Maker to implement the automatic methods that infer new mappings, which are propagated along the ontotologies [7]. Open research issues include: