Entity-relationship modeling is not only popular because of its graphical representations for structures, but also because of its treatment of semantics, which is rather simple compared with other database models such as the relational model, the network model or the hierarchical model. One lesson learned in the relational model is that it is not necessary to develop the theory of dependency classes and then apply it to the defined types. Instead, the semantic theory of types needs to be developed. ER modeling demands that a type is viewed as a whole item in the real world. For this reason, cardinality constraints must be specified not only for one particular relationship-entity association, but for the complete relationship type (may-be with the use of default assumptions in the case of missing specifications). This points directly to a principal advantage of ER modeling: Modeling a type as a complete item leads to a more complete specification. However for this reason, classical modeling methodologies cannot be applied in the same manner.
KeywordsFunctional Dependency Integrity Constraint Relationship Type Cardinality Constraint Implication Problem
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