SPATIO-TEMPORAL DATABASES Intro

“Space by itself, and time by itself, are doomed to fade away into mere shadows, and only a kind union of the two will preserve an independent reality.” (Albert Einstein)

Spatial and Temporal Databases In many activity areas, space and time are essential aspects. The applications have to process and query data that represents spatial and / or temporal characteristics of the managed objects. For example:  A GIS system (Geographic Information System) stores, analyzes and processes geographic data;  Files in a library must contain the details of borrowed and returned books. The objects that are managed by a GIS are spatial objects, and the information about the borrowed books from the library files is a temporal object (it has to be known for each book when was borrowed and when was returned).

Spatial and Temporal Databases As a first step, research in spatial and temporal areas was realized independently. Spatial databases have focused on modeling and querying geometries associated with objects, but keeping in the database the current status of spatial objects. Thus, spatial databases are static databases. Temporal databases, however, expanded the information in databases so that the previous states of objects were kept along with the current state of the modeled reality. The need to join spatial and temporal data in a single application arose as a natural fact.

Space & Time Space-Time similarities:  They are containers for objects (they include objects) – an object exists in space at a specific location and has a specific lifespan).  Both can be defined as metric or topological spaces.  As a structure, they can have discrete, dense or continuous domains.  The notions of “absolute” and “relative” exist in both areas. Space-Time differences:  In space, the motion can occur in any direction (random), but in time – is a one-way movement.  The time is dynamic, it is continuously flowing, but the space is static (as a container).  Usually, time is unlimited, and space is considered limited (in data modeling).  The relationships “<” or “  ” can be easily defined on a temporal axis, but not in a 2D or 3D space.  The space is physically limited to three dimensions, but the time has no such limitations (you can define many temporal axes).

Spatio-temporal Databases The ST objects are met very often in real life (also – domains where these objects are required to be managed):  history (migrations),  biology (monitoring the spread of flora and fauna in time),  volcanoes (the evolution of volcanic eruptions),  multimedia applications (the management of objects that appear and disappear in a presentation’s frames),  military operations,  weather systems,  transportation systems,  wireless networks etc.

The space-time continuum is the scene where all the physical events take place, where the evolution of all physical objects is recorded. The evolution of objects in space is given by the evolution line, surface, or volume (also known as world ‑ line for points, world ‑ sheet for lines, and world ‑ volume for regions, respectively).

Figure 1. Helix