Basic spatial events and their abstract data types in spatio-temporal data modeling

摘要

Time may be interpreted as a sequence of events. In a sense, spatial events indicate in-depth time semantics of spatial objects. As we know, complex spatial objects can be decomposed into three kinds of basic spatial objects: point, line and area. Various changes could be reduced to three kinds of basic changes: discrete change, stepwise change and continuous change. Thus, nine basic spatial events are derived. They are: (1) discrete change of point; (2) stepwise change of point; (3) continous change of point; (4) discrete change of line; (5) stepwise change of line; (6) continuous change of line; (7) discrete change of area; (8) stepwise change of area, and (9) continuous change of area. To model these basic spatial events in spatio-temporal databases, on the basis of point-string structured spatial data, nine abstract spatio-temporal data types and their data structures are proposed. These nine abstract spatio-temporal data types are : (a) discretely changing point CD Point, (b) stepwisely changing point SC Point, (c) continuously changing point CC-Point, (d) discretely changing line DC-Line, (e) stepwisely changing line SC-Line, (f) continuously changing line CC-Line, (g) discretely changing area DC-Area, (h) stepwisely changing area SC-Area, (i) continuously changing area CC-Area. They enrich time semantics of spatial data in spatio-temporal databases, and facilitate discretely and continuously time-varying spatial data modeling simultaneously. Meanwhile, a set of nine basic spatial events is more complete than sets of application-specific spatial events given by some scholars.