ER Modeling Review

Relatively simple representations of complex real world data structures

Data models
How to you determine the degree of a relationship

The number of entities involved in the relationship
How many instances of one entity can be involved with how many instances of another entity

Cardinality
A detailed, logical representation of the data for an organization or business area expressed in terms of Entity Types, Relationships and Attributes

ER Mode, ex. A CUSTOMER places an ORDER for a PRODUCT
To be an attribute it must be

A names property or characteristic of an entity type that is of interest to the organization
Simple attribute

Cannot be broken down into smaller components
Composite attribute

can be broken down into its component parts
Attribute that can be derived from related attribute value

Derived attribute
Unary - degree 1, also called bill of materials ore recursive
Binary, degree 2 most common
Ternary - degree 3
An entity that associates one or more entity types and contains attributes that tie the two instances together

Associative entity
How do you reduce the number of entities

If some entities have attributes in common we can generalize them into sets of entities, enhanced ER or EER

Author

Kimmiey

323371

Card Set

ER Modeling Review

Description

Updated

2016-09-20T00:01:53Z

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