2.9 - Generalised relationships

Generalised relationships describe the special case of having one entity of an ESet participating in only one of a set of possible relationships with other entities. Generalised relationships are represented with the notation shown in Figure 2.9.

Example

The diagram introduces a distinction between charged and neutral Clusters. Both Neutral and Charged have an additional attribute, CEnergy, containing a corrected energy. The Type attribute of Neutral contains a type of particle. Note that Tracks may be associated with Charged Clusters only.

Representation

Such generalized relationships are represented by an arrow with a broad tail that branches off in two or more regular arrows. The concepts of partiality, CardMin and CardMax apply equally to them. In the literature they are sometimes called Exclusive Relationships, and they can be used to represent not only object-oriented hierarchies of entities (as is the example) but also more complex situations.

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BR and MR - CERN PTG - ADAMO Users Guide for Version 3.3 - 11 Oct 93