A type of entity with a corresponding set of entities

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A type of entity with a corresponding set of entities: could be entity type, subclass, superclass, or category Note: The definition of relationship type in ER/EER should have 'entity type' replaced with 'class‘ to allow relationships among classes in general Subclass S is a class whose: Type inherits all the attributes and relationship of a class C Set of entities must always be a subset of the set of entities of the other class C S C C is called the superclass of S A superclass/subclass relationship exists between S and C Enhanced Entity-Relationship Modelling 35
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Formal Definitions of EER Model Specialization Z: Z = {S1, S2,…, Sn} is a set of subclasses with same superclass G; hence, G/Si is a superclass relationship for i = 1, …., n. G is called a generalization of the subclasses {S1, S2,…, Sn} Z is total if we always have: S1 S2 Sn = G; Otherwise, Z is partial. Z is disjoint if we always have: Si ∩ Sj empty-set for i ≠ j; Otherwise, Z is overlapping. Enhanced Entity-Relationship Modelling 36
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Formal Definitions of EER Model Subclass S of C is predicate defined if predicate (condition) p on attributes of C is used to specify membership in S; that is, S = C[p], where C[p] is the set of entities in C that satisfy condition p A subclass not defined by a predicate is called user-defined Attribute-defined specialization: if a predicate A = Ci (where A is an attribute of G and Ci is a constant value from the domain of A) is used to specify membership in each subclass Si in Z Note: If Ci ≠ Cj for i ≠ j, and A is single-valued, then the attribute-defined specialization will be disjoint. Enhanced Entity-Relationship Modelling 37
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Formal Definitions of EER Model Category or UNION type T A class that is a subset of the union of n defining superclasses D1, D2,…Dn, n>1: T (D1 D2 Dn) Can have a predicate Pi on the attributes of Di to specify entities of Di that are members of T. If a predicate is specified on every Di: T = (D1[P1] D2[P2] Dn[Pn]) Enhanced Entity-Relationship Modelling 38
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Alternative Diagrammatic Notations ER/EER diagrams are a specific notation for displaying the concepts of the model diagrammatically DB design tools use many alternative notations for the same or similar concepts One popular alternative notation uses UML class diagrams See next slides for UML class diagrams and other alternative notations Enhanced Entity-Relationship Modelling 39
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UML Example for Displaying Specialization / Generalization Enhanced Entity-Relationship Modelling 40
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Alternative Diagramma tic Notations Enhanced Entity-Relationship Modelling 41
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Knowledge Representation (KR) Deals with modeling and representing a certain domain of knowledge. Typically done by using some formal model of representation and by creating an Ontology An ontology for a specific domain of interest describes a set of concepts and interrelationships among those concepts An Ontology serves as a “schema” which enables interpretation of the knowledge in a “knowledge-base” Enhanced Entity-Relationship Modelling 42
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Knowledge Representation (KR) COMMON FEATURES between KR and Data Models: Both use similar set of abstractions – classification, aggregation, generalization, and identification.
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  • Fall '09
  • SUNANHAN
  • Entity-relationship model

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