Geoinformatics: Development of Community-Based Ontology and Standards for Hydrologic Data Discovery and Exchange

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The Consortium of Universities for the Advancement of Hydrologic Science, Inc. (CUAHSI) has been involved in the development of Water Data Services (WDS) through the CUAHSI Hydrologic Information Systems (HIS) project. The vision for WDS is to bring together the nation's (and, potentially, the earth's) water data in a federated system of servers linked using a services-oriented architecture. CUAHSI WDS is used by both academic researchers and by government data providers at both the Federal and State levels. A critical challenge in achieving this vision is understanding and reconciling structural and semantic differences across publishers of hydrologic data. The HIS project achieved interoperability between different data repositories by developing a common relational schema (Observations Data Model, ODM V1.1), an XML schema for exchanging hydrologic observations (Water Markup Language, WaterML V1.0), and a prototype ontology (V1.0) of hydrologic concepts that is used for data discovery purposes. Experience has shown that the prototypes for WaterML and the ontology are in need of further development. The prototype ontology provided semantic mediation among measured properties, but as this ontology was applied to more diverse data holdings, it became apparent that i) semantic heterogeneity continued to exist at various levels, including sampled media, sampling environment, chemical speciation, and units, that ii) the ontology needs to cover a wider range of parameters (such as those from the EPA Substance Registry System), and that iii) the development of semantic knowledge needs to be put on a much broader community base. WaterML has proven to be of great utility as a standardized way for transferring water information, but needs to be moved through a formalized standardization process. This project will address the underlying semantic problem through the development of a more comprehensive, extensible ontology that harmonizes the more generic information model contained within ODM with those from various existing federal information sources. This includes the development of a community process for an evolving hydrologic ontology. In addition, WaterML, which has been adopted by USGS and NCDC, will be extended to reflect this more generic information model. The project will contribute to forming an international standard. The fundamental goal of the project is the organization of hydrologic concepts in a way that allows publishers to describe their data unambiguously and helps users to discover data easily yet with a precise understanding of the properties measured and their context.