Spatial information is a common component of databases maintained by state and federal governments, research organizations, and public policy institutes. Federation of these data sources allow policy makers to issue queries against multiple data sets across organizational and geographic boundaries to provide a more complete and more up-to-date view of the results. For data providers, federation provides a means to publish their data sets while maintaining ownership of the data (access control, update control, accounting, etc). Application developers also benefit by being able to build applications that automatically discover the available data sets and compute resources. A system with these capabilities, called the "Geon Grid system", is currently being built as part of the GEON project. We present this approach to information integration across spatial sources, providing architecture and implementation details of a grid services-based wrapper-mediator system.

Our basic architecture follows the common wrapper-mediator model where system components exchange messages in the form of virtual XML documents. Source schemas and capability descriptions are exposed to the mediator in the process of source registration, but the source data sets always reside within the owners domain. Users can pose queries against the integrated view maintained by the mediator from a specially designed mapping interface. The system manages the availability and performance of the data access through staging, caching and replication of the data sets. Each source wrapper exposes a standard interface to the mediator built around WSDL source descriptions. In addition to source wrapping, a variety of data conversion services including type conversion, coordinate conversion, concept resolution and spatial results assembly services are built into the system. All system components and services are built using grid and web services standards, thereby leveraging the common core capabilities and developer tool support. We will present how these grid technologies are being used in the GEON project with specific applications related to state geologic data set integration.