Using a hydro-reference ontology to provide improved computer-interpretable semantics for the groundwater markup language (GWML2)

ABSTRACT Comprehensive water data management requires semantically integrating various data models and ontologies that represent hydrologic knowledge. But integration is hampered by nuances in the use of water-related vocabulary (e.g. terms such as water body, aquifer, reservoir, well, etc.) across water representations and by the reliance on a mix of formal and informal specifications of how these terms are interpreted in each representation. Reconciliation of only partially formal encodings of the semantics of water representations requires manual inspection using tools from ontological analysis. This paper investigates as to what extent a domain reference ontology that is fully formalized in first-order logic can guide the ontological analysis. In particular, it is studied as to what extent the Hydro Foundational Ontology (HyFO), which encodes the semantics of a small set of unifying water concepts and associated relations in first-order logic, can serve as a reference ontology for the water domain to steer the ontological analysis of individual water representations, and to formalize their semantics more fully. This is specifically tested on the Groundwater Markup Language (GWML2). The result is GWML2-FOL, a concise logical description of GWML2’s key terms as a logical extension of HyFO. GWML2-FOL is structured into three layers of terms (mostly classes) of increasing specificity. The top layer consists of terms shareable across the earth and physical sciences, an intermediate layer includes HyFO’s hydro terms that span surface and subsurface water storage, and the bottom layer encapsulates groundwater specific GWML2 terms. The analysis and stratification uncover semantic ambiguities in GWML2 and suggest terminological and semantic clarifications and modifications in preparation for integrating GWML2 with other semantic water representations. The analysis also identifies two necessary additions to the HyFO: the concept of a hydro rock body as a hybrid of water and solid matter, which generalizes key groundwater terms such as aquifers or wells, and the concept of dependent hydrologic features such as springs, water tables, or divides. More broadly, differences between domain ontologies and a domain-reference ontology and their respective complementary roles in semantic-enabled geosciences are outlined.