Valences. A new relationship concept for the entity-relationship model

Semantic data models for engineering applications often employ the Entity-Relationship approach in some variation, today mostly combined with an object-oriented flavor. The database community meanwhile agrees on the notion of entities as units with a unique identification and some attributes. But as far as relationships are concerned, there is no generally accepted model up to now; this is illustrated by the large number of different definitions of the term "complex object". This paper describes the so-called valence concept, a general method to specify relationships. This approach is type-based, admits variants and detailed cardinality specifications, and can cope with incomplete intermediate states. Nevertheless, the resulting type definition syntax is easy to understand. The valence concept is introduced in an informal way first. then a formal definition is presented, and it is outlined that an implementation of the concept can be efficient both in space and time. The valence concep t proposed here is not a complete data model, but a relationship model, which has to be embedded in a data model. As such, it is part of the GEMINI system which is under development at FhG-AGD.