An object-oriented shared data model for GIS and distributed hydrologic models

Distributed physical models for the space–time distribution of water, energy, vegetation, and mass flow require new strategies for data representation, model domain decomposition, a priori parameterization, and visualization. The geographic information system (GIS) has been traditionally used to accomplish these data management functionalities in hydrologic applications. However, the interaction between the data management tools and the physical model are often loosely integrated and nondynamic. This is because (a) the data types, semantics, resolutions, and formats for the physical model system and the distributed data or parameters may be different, with significant data preprocessing required before they can be shared; (b) the management tools may not be accessible or shared by the GIS and physical model; and (c) the individual systems may be operating system dependent or are driven by proprietary data structures. The impediment to seamless data flow between the two software components has the effect of increasing the model setup time and analysis time of model output results, and also makes it restrictive to perform sophisticated numerical modeling procedures (real-time forecasting, sensitivity analysis, etc.) that utilize extensive GIS data. These limitations can be offset to a large degree by developing an integrated software component that shares data between the (hydrologic) model and the GIS modules. We contend that the prerequisite for the development of such an integrated software component is a ‘shared data model’, which is designed using an object-oriented strategy. Here we present the design of such a shared data model taking into consideration the data type descriptions, identification of data classes, relationships, and constraints. The developed data model has been used as a method base for developing a coupled GIS interface to Penn State Integrated Hydrologic Model (PIHM), called PIHMgis.