ABSTRACT
Such data has to be integrated into the context o f time, a capability that the con
ventional database management systems do not have. In the meantime, numerous
proposals have been made along this line which include the time to be stored as a
universal attribute. The attribute itself can, for instance, be transaction time, valid
time, or any user-defined time. Recently, four types o f time related databases have
been defined according to their ability to support the time concepts and to process
temporal information:
• Snapshot databases, i.e. databases that give an instance or a status o f the data stored concerning the system (plant, enterprise) at a certain instant o f time, but not necessarily corresponding to the current status o f the sys tem. By insertion, deletion, replacement and similar data manipulation a new snapshot database can be prepared, reflecting a new instance or state o f the system, whereby the old one is definitely lost.
