Moving Objects Databases

Abstract

Each moving objects database represents the trajectory and speed of moving objects. In all moving objects reprentations the spatial and the temporal extents of the objects depend on each other. This is in contrast to some earlier data models, such as, the rectangles and the Worboys data models, that had spatial and temporal extents that were independent of each other. Therefore, the earlier data models could only represent objects that appear and disappear suddenly. Hence they cannot represent continuously moving objects. In this chapter we introduce several moving objects data models that generalize some of the earlier seen geographic data models by the use of an extra time parameter t allowing the expression of linear, polynomial, or periodic functions of time to extend a static space to a continously moving space. Section 7.1 describes moving points, which are the simplest and most common of the moving objects data models. Unfortunately, moving points are limited because they cannot represent the shape of the objects. Section 7.2 presents the parametric circles data model. This data model advanced the moving points data model by approximately representing the shape of the moving objects as circles that can change their sizes. Section 7.3 describes parametric rectangles, while Section 7.4 describes the parametric Worboys data model. These generalize the rectangles and the Worboys data models, respectively, by representing the endpoints of rectangles or triangles using parametric functions of time. Section 7.5 further generalizes these two parametric extreme points data models by allowing periodic functions.