Extended Entity-Relationship Model
نویسنده
چکیده
DEFINITION The extended entity-relationship (EER) model is a language for definition of structuring (and functionality) of database or information systems. It uses inductive development of structuring. Basic attributes are assigned to base data types. Complex attributes can be constructed by applying constructors such as tuple, list or set constructors to attributes that have already been constructed. Entity types conceptualise structuring of things of reality through attributes. Cluster types allow the generalise or to combine types into singleton types. Relationship types associate types that have already been constructed into an association type. The types may be restricted by integrity constraints and by specification of identification of objects defined on the corresponding type. Typical integrity constraint of the extended entity-relationship model are participation, lookup and general cardinality constraints. Entity, cluster and relationship classes contain a finite set of objects defined on these types. The types of an EER schema are typically depicted by an EER diagram.
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