| In this dissertation, we extend database models and query languages to support spatio-temporal information, including representations for changing positions and shapes. Furthermore, we propose techniques to support spatio-temporal extensions on Object-Relational systems and achieve end-user extensibility.; We begin from temporal data models and query languages. Our approach is based upon a point-based representation of time enhanced with user-defined aggregates that support interval-oriented operators such as DURATION and DURING. This approach provides several advantages, since it solves the coalescing problem, minimizes extensions required from SQL, and it is applicable to all query languages.; Then, we extend the time model at the physical level to spatio-temporal databases. As the basis of our implementation, we introduce counterclockwise-directed are introduced to support spatial operators such as CONTAIN and OVERLAP, and spatial-temporal operators such as MOVING_DISTANCE. Finally, we represent moving objects as sequences of snapshots of spatial objects such as points, lines and polygons.; To reconcile logical and physical requirements, we follow an implementation approach based on a layered architecture. Thus, for temporal information, point-based representations are mapped to an interval-oriented representation at the internal level. Likewise, we map polygon-based representations into a triangle-based internal representation. We implement these mappings through query transformations, and user-defined aggregates.; A final advantage of our approach is that it allows end-users to further extend and customize their system: in fact in our SQLST system, users can extend database functionality by writing new user-defined aggregates in SQLST itself.; In summary, the spatio-temporal data models and query languages introduced in this dissertation offer several conceptual advantages; furthermore, our implementation approach provides considerable practical benefits, including compatibility with Object-Relational systems, flexibility, robustness, and ease of customization by end-users. |
