Identity-based change: a foundation for spatio-temporal knowledge representation

As efforts grow to develop spatio-temporal database systems and temporal ge ographical information systems that are capable of conveying how geographic al phenomena change, it is important to distinguish the elements that are f undamental to scenarios of change. This paper presents a model based on the explicit description of change with respect to states of existence and non -existence for identifiable objects. Such changes are of concern when, for instance, modelling and reasoning about nations that are subsumed through c onflict only to return once more at a later time, or about water bodies tha t fluctuate due to seasonal or climatic change. The basis for tracing these changes is the concept of object identity. Identity, distinct from an obje ct's properties, values, or structure, is that unique characteristic that d istinguishes one object from another. Based on a small set of primitives re lating to the identity states of objects, we model the semantics associated with change and through a systematic derivation, a complete set of identit y-based change operations evolves from the primitives. These operations are basic to the types of change commonly experienced by geographical phenomen a and modelled by researchers studying spatio-temporal change. This approac h highlights the minimum elements necessary for reasoning about change, nam ely, object identity, an ordering of identity states, and co-occurrence of identity states.