Database Reference
In-Depth Information
3
Trajectory Databases
Ralf Hartmut Guting, Thomas Behr, and Christian Duntgen
3.1 Introduction
In this chapter, we consider the problem of modeling and representing trajecto-
ries in the context of database systems. Since about 1995 there has been research
on
moving objects databases
(MODs), also termed
spatio-temporal databases
.
The general goal has been to allow one to represent moving entities in data-
bases and to enable a user to ask all kinds of questions about such movements.
This requires extensions of the DBMS data model and query language. Further,
DBMS implementation needs to be extended at all levels, for example, by pro-
viding data structures for representation of moving objects, efficient algorithms
for query operations, indexing and join techniques, extensions of the query opti-
mizer, and extensions of the user interface to visualize and animate moving
objects.
Moving objects databases come in two types. The first represents a set of
currently moving objects. One is interested in maintaining the current locations
and asking queries about current and expected near future locations. The second
type maintains complete histories of movement. These are sometimes called
trajectory databases
and are the topic of this chapter.
Whereas spatio-temporal databases had been around for a much longer time,
they supported only discrete changes of geometries over time. The empha-
sis in the new field of moving objects databases is to consider
continuously
changing geometries
. Neither the position of a car on a road nor the shape and
location of a hurricane changes in discrete steps; these are clearly continuous
phenomena.
A driving force in the development of database systems has always been
to provide to the user a simple conceptual model of data. Relational databases
have been so successful because they introduced the simple view of representing
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