A Comparison of Three Systems Modeling Methodologies - High-Performance Web Databases: Design, Development, and Deployment - page 197

Exhibit 13-4. Diagram notation for shlaer and mellor's information model.
Different categories of attributes include descriptive attributes, naming
attributes, referential attributes and identifier attributes. Descriptive
attributes provide basic facts about each instance of an object. Examples
are the salary and address of an employee object.
An identifier attribute is an attribute or combination of attributes that
uniquely distinguishes one instance of an object from another. An identifier
is sometimes called a candidate key. An example of identifier attributes are
the state and title number for a car object. Neither attribute alone is suffi-
cient to uniquely identify an instance of a car. Referential attributes are those