OnGIS: Ontology-Based Geospatial Data Integration and Retrieval

Abstract

Querying geospatial data from multiple heterogeneous sources backed by different management technologies poses an interesting problem in the data integration and the subsequent result interpretation. I propose two ways of entering complex spatial queries in a user-friendly way and broker techniques for answering a query by finding relevant data sources (from a catalogue) capable of answering the query, eventually splitting the query and finding relevant data sources for the query parts, when no single source suffices. For expressing data source capabilities, I describe each source with a set of prototypical queries that are algorithmically arranged into a lattice, which makes searching efficient. The proposed algorithms leverage GeoSPARQL query containment enhanced with OWL 2 QL semantics. Using GeoSPARQL as both the querying language and the language for expressing capabilities gives the flexibility to incorporate many heterogeneous geospatial data sources, no matter what storage, data model, or terminology they use. All parts of the design are presented in a prototype called OnGIS, which implements the proposed methods of entering a user query, searching for the relevant data sources, and translating the query to requests the underlying data source technologies understand.