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11 Cards in this Set
- Front
- Back
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What is an entity?
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An entity is an existing physical or conceptual object that can be distinguished from other objects
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What is an entity type?
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An entity type is an abstract description of the common characteristics of similar entities
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What is an entity set?
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An entity set is the set of the entities, which conform to the definition of an entity type and therefore could be considered as instances of this type
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What is a relationship?
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A relationship is an association among two or more entities
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What is a relationship type?
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A relationship type is an abstract description of similar relationships among entities of the same entity types
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What is a relationship set?
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A relationship set is the set of the relationships, which conform to the definition of relationship type and therefore could be considered as instances of this type
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What is an attribute?
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An attribute is a characteristic (property) of an entity or a relationship
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What types of values can attributes take?
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Attributes may take one or more primitive or composite values
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What is a key (or superkey)?
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A key (or superkey) is a minimal set of one or more attributes, which collectively identify the individual entities and relationships in the extensions of entity and relationship types
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What is a candidate key?
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A candidate key is a distinct collection of attributes that may serve as a key
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What is a primary key?
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A primary key is a candidate key chosen by a database designer to be the key for an entity or relationship type
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