Entity Relationship Schema Flashcards

1
Q

Entities

A

The Box
A thing which can be distinctly defined.

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2
Q

Relationship

A

Diamond
Association between entities.

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3
Q

Attribute

A

Oval
Common properties shared by all instances of an entity type.

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4
Q

Simple Attribute

A

Has one component, so a first name.

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5
Q

Complex Attribute

A

Have a structure
A full name would be a complex attribute.

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6
Q

Primitiveness

A

An attribute which will be stored in the system as data.

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7
Q

Degree

A

Number of entity types in a relationship, which can have a constraint.

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8
Q

Cardinality

A

One to many, many to many etc.
One person can have many emails.

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9
Q

Participation

A

A participation constraint specifies whether an entity must
be in the given relationship

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10
Q

Weak Entity Type

A

Cannot be identified with isolation.
Represented by double box.

The front desk -> cannot be identified.
The front desk at Ashton Theatre -> is now identified.

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11
Q

Strategies for ER design

A

Top-down - start with schema containing high-level abstractions and work down
Bottom-up - start with schema containing basic-level abstractions and work up
Inside-out - start with central concepts

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12
Q

Identifying Relationship

A

Used for weak entities to demonstrate that this relationship defines an entity
Double diamond.

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13
Q

Key Attribute

A

Oval with Line
Identifies the entity.

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14
Q

Derived Attribute

A

Dotted Circle
Does not exist in the physical database, but their values are derived from other attributes present in the database.

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