The Object Event Calculus and Temporal Geographic Information Systems
NAVAL RESEARCH LAB STENNIS SPACE CENTER MS MARINE GEOSCIENCES DIV
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Extension of the temporal database model into the object-oriented database paradigm requires re-assessment of the temporal issues familiar in the RDBMS world. For example the debate on timestamping relations or individual tuples is mirrored in the question of at what level to apply a timestamp to a temporal object. A brief review of temporal issues as applied to object-oriented databases is supplied. In our approach, the Event Calculus is used to provide a formalism that avoids the question of object timestamping by not applying time to objects. Rather, temporal behavior is reflected in events, which bring about changes in objects. Previous applications of the Event Calculus in databases are considered. An extension of the formalism to a fully bitemporal model is demonstrated. These extensions and the Object Event Calculus OEC form a framework for approaching temporal issues in Object-oriented systems. Practical application issues, as well as formal theory are described an implementation in Java code for the Event Calculus is discussed. Current GISes will support a real calculations on geographic objects, and can also describe topological relations between them. However, they lack the ability to extrapolate from historical data. The sufficiency of the temporal GIS model to support inventory, updates, quality control and display is demonstrated. Follow-up and further extensions and areas of exploration are presented at the conclusion.
- Information Science
- Computer Programming and Software