each target entity is referenced Car has Manufacturer Car 11 0n has

Each target entity is referenced car has manufacturer

This preview shows page 102 - 115 out of 358 pages.

(each target entity is referenced) Car has Manufacturer Car [1..1] [0..n] has Manufacturer Alternative for: Schallehn (FIN/ITI) Advanced Database Models 2019 102 / 358
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ER Model: Unary Relationship Self-referential on type-level Different instances of the same type are related Person [0..1] [0..1] married to Husband Wife Schallehn (FIN/ITI) Advanced Database Models 2019 103 / 358
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ER Model: N-ary Relationship Relationship type might involve more than 1 or 2 entity types Example for ternary relationship type Lecturer teaches Course Room Schallehn (FIN/ITI) Advanced Database Models 2019 104 / 358
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ER Model: N-ary Relationship /2 N-ary relationship type can not be replaced by n binary relationship types Semantics of following example different from previous: allows lecturers to use rooms without a course taking place Lecturer teaches Course Room takes place uses Schallehn (FIN/ITI) Advanced Database Models 2019 105 / 358
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ER Model: Weak Entity Types Existential dependency to other entity Types Identity (key attribute) includes key of master entity type Relationship between weak entity type and its master type is called identifying relationship Building N 1 has Room Schallehn (FIN/ITI) Advanced Database Models 2019 106 / 358
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Basic Extensions to the ER Model Total or partial participation Complex attributes Derived attributes Multi-valued attributes Schallehn (FIN/ITI) Advanced Database Models 2019 107 / 358
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ER Extensions: Total Participation Each entity of one type must relate to at least one of the other entity type at least once Graphical notation: thick or double line Difference to functional relationship: entity may participate in relationship several time Student of University Alternative for: Student [1..n] [0..n] of University Schallehn (FIN/ITI) Advanced Database Models 2019 108 / 358
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ER Extensions: Partial Participation Standard case: each entity of one type may or may not relate to one or more entities of the other entity type Graphical notation: thin line Optional N:M-relationship Person owns Car Alternative for: Person [0..n] [0..n] owns Car Schallehn (FIN/ITI) Advanced Database Models 2019 109 / 358
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ER Extensions: Complex Attributes Composite attributes consisting of atomic attributes of different types Person SSN Name Address City Street ZIPcode Schallehn (FIN/ITI) Advanced Database Models 2019 110 / 358
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ER Extensions: Multi-valued Attributes Composite attributes consisting of variable set of values of the same type Person SSN Name PhoneNumbers Schallehn (FIN/ITI) Advanced Database Models 2019 111 / 358
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ER Extensions: Complex Attributes Virtual attribute with value that can be computed from other attributes or via relationships Person SSN Name Age BirthDate Schallehn (FIN/ITI) Advanced Database Models 2019 112 / 358
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Basic ER Extensions Summary Only most common extensions were introduced here Many others exist in books and DB design tools Many different notations exist for the same concepts Schallehn (FIN/ITI) Advanced Database Models 2019 113 / 358
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Object-oriented Extensions to the ER Model Specialization as the derivation of sub-types I Semantic concept of the is_a -relationship I Various notations exist I
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