Databases Reference
In-Depth Information
between several different events. Their number increases is inverse proportion to
the level of consideration, i.e. the lower is the level, the more are the repeating sub-
events. Keeping the number of redundancies as small as possible is a major
characteristic of the database systems, so avoiding such a big number of repetitions
of the same event is an important criterion. One possible solution is to allow each
event to be regarded as a part of several higher level events. Therefore, the
appropriate structure which fits to the above conditions appears to be a hierarchical
network. In Figure.7 is shown a concrete example. Choosing network as a basic
structure for describing events imposes some special requirements on the data
model and database query language. The data model should provide simple and
natural mapping of the hierarchical network into the data model primitives.
Figure 6: An Example of Event Model
Figure 7: Event Tree
