Query operations for moving objects database systems

Abstract

Geographical Information Systems were originally intended to deal with snapshots representing a single state of some reality but there axe more and more applications requiring the representation and querying of time-varying information. This work addresses the representation of moving objects on GIS.The continuous nature of movement raises problems for representation in information systems due to the limited capacity of storage systems and the inherently discrete nature of measurement instruments. The stored information has therefore to be partial and does not allow an exact inference of the real-world object's behavior. To cope with this, query operations must take uncertainty into consideration in their semantics in order to give accurate answers to the users.The paper proposes a set of operations to be included in a GIS or a spatial database to make it able to answer queries on the spatio-temporal behavior of moving objects. The operations have been selected according to the requirements of real applications and their semantics with respect to uncertainty is specified. A collection of examples from a case study is included to illustrate the expressiveness of the proposed operations.

Location-dependent query processing

“…In Trajcevski et al 2004b], the modifiers proposed are called possibly and definitely. In [Moreira et al 2000], three semantics are distinguished: possibly (equivalent to may), surely (equivalent to must/definitely), and probably (where locations are estimated and so the results can contain false hits and also be incomplete). Section 4.1.4 indicates several works where the uncertainty of locations and probabilistic versions of location-dependent queries are considered.…”

Evaluation of probabilistic queries in moving objects databases

“…The second approach [9,8] focuses on past movements. It addresses the needs of mining applications of spatiotemporal data: traffic mining, environment monitoring, etc.…”

“…The radius of circle in the left is ra = Vmax × (t b − t0) and for circle in the right is r b = V max × (t 1 − t a ). For a detailed explanation of these formulas please refer to [8]. Considering that we have methods that allow estimating probabilities about the location of a moving object at any time instant, the evaluation of spatiotemporal query expressions could than be augmented with probabilistic estimates about the validity of answers to users queries.…”

Efficient Security Policy Enforcement in a Location Based Service Environment

“…Considering the basic authorization specification subject, object, privilege , in a mobile environment, a moving object can be a subject, an object, or both. Access requests in such an environment can typically be on past, present and future status of the moving objects [2,3]. Serving an access request requires to search for the desired moving objects that satisfy the query, as well as enforce the security policies.…”