An object-oriented approach to the representation of spatiotemporal geographic features

Abstract

Geographic features change over time, this change being the result of some kind of event or occurrence. It has been a research challenge to represent this data in a manner that reflects human perception. Most database systems used in GIS are relational, and change is either captured by exhaustively storing all versions of data, or updates replace previous versions. This stems from the inherent difficulty of modelling geographic objects in relational tables. This difficulty is compounded when the necessary time dimension is introduced to model how those objects evolve. There is little doubt that the object-oriented (OO) paradigm holds significant advantages over the relational model when it comes to modelling real-world entities and spatial data, and we believe that this contention is particularly true when it comes to spatiotemporal data. In this paper, we describe a generic, object-oriented model for representing spatiotemporal geographic data, called the Feature Evolution Model (FEM), based on a 'state-event-state' approach. The model exploits the expressiveness of OO technology by representing both geographic entities and change as objects, and the potential complexities introduced by the temporal elements of change are minimised by subtyping. The conceptual model is represented using UML and has the advantage of being implementable by any OO programming language and database development environment. The generic model is applied to real-world geographic data, that of OS MasterMap Integrated Transport Network (ITN) data.