ER Flashcards Preview

Databases > ER > Flashcards

Flashcards in ER Deck (11):
1

Attributes

Property of an entity

2

Entity

A collection of attributes

3

Domain

Set of values for an attribute

4

Multi-valued Attribute

A list of attributes {7734, Plumb Rd, Galena, Oh, 43021}

5

Composite Attribute

An organized list of attributes {Name} -> {Gabe, Steppers}

6

Derived Attributes

Not stored, but calculated on request

7

Cardinality

Relationships:

1:1, 1:n, m:n

Employee --N-- -----1---- Project

The project can have many employees.
The employee can have one project.

8

Total Participation

Means that the entity MUST be present.

For Chen Notation this is represented by double lines on the side of participation (opposite of carnality)

9

Weak Entities

Cannot be identified on their own, dependent on a strong entity. Can have partial keys.

10

Binary Relationship

Employee ----n----- ------1------ Project

Single mapping between employee and project

11

Ternary Relationship

Employee ----n------ ------1-----Project
|
|
|
Salary

More thing two mappings in a relationship, should be shied away from