A foundation for representing and querying moving objects

Spatio-temporal databases deal with geometries changing over time. The goal of our work is to provide a DBMS data model and query language capable of handling such time-dependent geometries, including those changing continuou sly that describe moving objects. Two fundamental abstractions are moving p oint and moving region, describing objects for which only the time-dependen t position, or position and extent, respectively, are of interest. We propo se to represent such time-dependent geometries as attribute data types with suitable operations, that is, to provide an abstract data type extension t o a DBMS data model and query language. This paper presents a design of suc h a system of abstract data types. It turns out that besides the main types of interest, moving point and moving region, a relatively large number of auxiliary data types are needed. For example, one needs a line type to repr esent the projection of a moving point into the plane, or a "moving real" t o represent the time-dependent distance of two moving points. It then becom es crucial to achieve (i) orthogonality in the design of the type system, i .e., type constructors can be applied uniformly; (ii) genericity and consis tency of operations, i.e., operations range over as many types as possible and behave consistently; and (iii) closure and consistency between structur e and operations of nontemporal and related temporal types. Satisfying thes e goals leads to a simple and expressive system of abstract data types that may be integrated into a query language to yield a powerful language for q uerying spatio-temporal data, including moving objects. The paper formally defines the types and operations, offers detailed insight into the consider ations that went into the design, and exemplifies the use of the abstract d ata types using SQL. The paper offers a precise and conceptually clean foun dation for implementing a spatio-temporal DBMS extension.