Spatial Data Modelling, Dual Partitions and the Specification of Semantics

The main objective of GSDI is data sharing and integration. This requires the formulation of standards for data exchange. Most standards developed to date take mainly care of issues like the technical specification of spatial data structures, spatial operators and meta data. Even with these standards the user community will face significant problems in data sharing because hardly any standards are provided yet with respect to the semantic aspects of geo-information. Semantics is generally embedded in specific application contexts so that knowledge of such a context is a prerequisite for understanding the semantics of data. Yet some of the formal and theoretical aspects of spatial data modelling will be guiding the specification of data semantics, so that a proper understanding of these aspects will be essential in this respect. These issues will be discussed in this presentation. A mathematical formalization allows the formulation of rules for specifying spatial data models relating thematic and geometric data, based on the combination of spatial and thematic partitions. This dual partition structure can be seen as a constraint for unambiguous semantic specifications; this constraint implies the direct relationship between thematic and spatial object descriptions. Furthermore if we require that semantic specification of spatial data should always comply with this constraint then it should be maintained under the process of object aggregation or data generalization. This implies that semantic specifications of spatial objects can (or should) generally be understood in a multi aggregation (or multiscale) context.