Entity Relational Model Flashcards

(11 cards)

1
Q

Entity

A

Object of interest to the end user (effectively a table)

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2
Q

Entity Instance / Occurance

A

A row - or a tuple

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3
Q

Attribute

A

Characteristics of an entity (a field)

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4
Q

Composite Attribute

A

Attributes that can be subdivided into additional attributes (i.e address into number, street, postcode, state)

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5
Q

Multivalued Attributes

A

Attributes that can have many values (e.g. 1 person, many degrees)

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6
Q

Derived Attributes

A

An attribute whose value can be directly derived from other attributes

doesn’t need to be stored as an attribute, can be calculated on the fly

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7
Q

Domain

A

Set of possible values that an attribute can have

different attributes can share the same domain - e.g. the professor and student address will likely share the same domain

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8
Q

Identifiers (+ important tip with PK)

A

Attributes that can be used to uniquely identify an entity instance

(important - in conceptual designs you never refer to them as a primary key, this is an implementation detail)

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9
Q

Composite Identifier

A

Identifiers that are made up of two or more attributes - so it requires a unique combination of these elements

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10
Q

Degree

A

Number of attributes in an entity

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11
Q

Cardinality (in an entity)

A

Number of rows in a table

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