SQL~(ST): A Spatio-Temporal Data Model and Query Language

摘要

In this paper, we propose a query language and data model for spatio-temporal information, including objects of time-changing geometry. Our objective is to minimize the extensions required in SQL, or other relational languages, to support spatio-temporal queries. We build on the model proposed by Worboys where each state of a spatial object is captured as a snapshot of time; then, we use a directed-triangulation model to represent spatial data, and a point-based model to represent time at the conceptual level. Spatio-temporal reasoning and queries can be fully expressed with no new constructs, but user-defined aggregates, such as AREA and INSIDE for spatial relationships, DURATION and CONTAIN for temporal ones, and MOVING-DISTANCE for spatio-temporal ones. We also consider the implementation problem under the assumption that, for performance reasons, the representation at the physical level can be totally different from the conceptual one. Thus, alternative physical representations and mappings between conceptual and physical representations are discussed.