Computer Sciene of Udayana State University

April 18, 2009

Attribute

Filed under: Computer Science — ignaga @ 11:47 AM

· Characteristics of entities

· In Chen model, attributes are represented by ovals and are connected to entity rectangle with a line

· Each oval contains the name of attribute it represents

· In Crow’s Foot model, attributes are written in attribute box below entity rectangle

· Should be meaningful

· Rule of thumb is to prefix attribute with entity name

i.e. CUSTOMER_NAME versus NAME

· Can be single valued

An attribute that can have only a single value

i.e. social insurance number

· Can be multi valued

An attribute that can have many values

i.e. an employee has many skills

Derived Attributes

· Attribute whose value may be calculated (derived) from other attributes

· Need not be physically stored within database

· Can be derived by using an algorithm

· Can show in the conceptual model

Null Value Attribute

· Attribute that doesn’t have any value for a record

Mandatory Value Attribute

· Attribute that must have a value

Advertisements

Leave a Comment »

No comments yet.

RSS feed for comments on this post. TrackBack URI

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Blog at WordPress.com.

%d bloggers like this: