Identity-based reasoning about spatiotemporal change
Max J. Egenhofer, Kathleen Hornsby · 1999
Geographic Information Systems (GISs) are a special type of information system that store, convey, analyze, and manipulate geographic data. From their roots in modeling spatial aspects of the world, GISs are now being called upon to convey scenarios like those people experience everyday—i.e., scenarios that vary over time as well as space and involve phenomena that undergo change. Current GISs, however, require extensions in order to treat time and change and fall short of capturing the rich and often complex ways in which phenomena change. This thesis presents a systematic treatment of change as it applies to modeling the existence or non-existence of identifiable, discrete objects. It distinguishes the fundamental components of change that are independent of a particular scenario. This is achieved by developing a model of change based on the concept of tracking alterations to an object's identity. Identity distinguishes an object from all others, capturing an object's uniqueness and individuality. By developing such a model, this research effort highlights important semantics associated with these changes fundamental to those commonly experienced by geographic phenomena and modeled by researchers. The systematic approach to describing identity-based changes ensures that a complete set of change operations is distinguished. The results of this thesis show that an identity-based approach to modeling change captures additional semantics that are otherwise unobtainable by more traditional temporal database approaches. Furthermore, no spatial aspects need be explicitly represented with the identity-based model to achieve useful temporal reasoning about many scenarios of change. Instead, modeling changes to objects requires only dime basic elements: object identity; an ordering of change operations; and co-occurrence of identity states (i.e. simultaneous change). This frees modelers, for instance, from having to ground their representations to some time-line or from requirements for specification of detailed spatial or temporal aspects that might not be available or relevant to the task at hand.