A descriptor of an entity type. Attribute types are the names of the things the business must store about entity types.
For example, the entity type EMPLOYEE may be described by attribute types Employee Name, Employee Number, Birth Date, Sex, Height and Eye Color.
An individual entity of the type EMPLOYEE may be described as J. Frost, 3142, 5 April 1959, Male, 72, Blue. This description consists of values of the above attributes.
Entity types, therefore, are described by attribute types, and entities are described by attribute values.
Attribute Type Source
The categorization of an attribute type according to whether its values are basic, derived or designed.
Attribute Type Source Categories
It is useful for the verification and selection of attributes, and for later program and data design, to record the source category of an attribute. There are three possible source categories:
* Basic Attribute: An attribute type whose values cannot be calculated. Its values must be entered into the database (e.g., Employee Name, Birth Date)
* Derived Attribute: An attribute type whose values can be calculated from attribute values available in the database (e.g., Invoice Value, Account Balance, Pension Contribution)
* Designed Attribute: An attribute type whose value is calculated to serve a particular purpose and has no specific meaning to the enterprise (e.g., Abbreviated Customer Name, Employee Number)
Designed attributes types are not business objects and so are generally best avoided during Business Area Analysis. You may need them occasionally, when there is no other way of identifying the entities of an entity type (e.g., Employee Number), or when they are imposed by an external authority (e.g., Postal Code/Zip Code).
Fixed Attribute Type
An attribute whose values, once established for any given entity, remain unchanged for the life of that entity.
Composite Attribute Type
A named collection of attribute types of one entity type in which each group of values may be treated as if it were a single value.
An attribute type may consist of a meaningful collection of other attribute types. For example, the attributes Birth Month, Birth Day and Birth Year comprise the attribute type Birth Date, which is meaningful to the business and may be handled as a single attribute type. Birth Date is therefore described as a composite attribute type.
Optional Attribute Type
An attribute type that need not have a value for every entity of the type it describes.
When an entity need not have a value for a particular attribute, that attribute is optional. For example, the entity type LOCATION has an attribute of Telephone Number, but not every LOCATION has a telephone. Any such LOCATION will have no value for the Telephone Number attribute.
The optionality of an attribute may depend on a defined condition (e.g., BOOK has a Price only if it is still in print).
Optionality may depend on the existence of a relationship membership (e.g., EMPLOYEE has Pension Contribution only if EMPLOYEE participates in a PENSION SCHEME). The conditions and condition logic for attributes are basically the same as for relationships. They are a type of predicate condition and have predicate condition logic.
Transient Attribute Type
An attribute type whose values may change several times during the life of the entity that each value describes.
Previous : Activity
Section Overview : Development Technique Concepts
Overview : Table of Contents
This page was last built on April 12, 1997.