A Comparison of Three Systems Modeling Methodologies - High-Performance Web Databases: Design, Development, and Deployment - page 202

Exhibit 13-7. OMT diagram of an accounting system.
means if object A is part of object B and object B is part of object C, then
object A is part of object C. Asymmetric means that if object A is part of
object B, then object B is not part of object A.
Another important concept in the object model is generalization. In OMT,
it is defined as the relationship between a class and one or more refined ver-
sions of the class. Generalization is also called an is-a relationship. An impor-
tant property of generalization is inheritance. Inheritance is the sharing of
attributes and operations among the classes in a generalization hierarchy.
These features are inherited from a superclass by its subclasses.
Exhibit 7 illustrates these concepts in an OMT object diagram of an
accounting system. The diagram contains a Supplier, Account, Payment,
Pay_Method, Check, Credit_Card, and Cash objects. The Account must have
a single Supplier. The Supplier object charges one or more Accounts. The
Account object is associated with zero or more Payment objects. The Pay-
ment object pays one or more Accounts. There is a link attribute associated
with the Account and Payment objects. This link attribute occurs because of
the amount attribute associated with the many-to-many relationship between
the Payment and Account objects. There is a one-to-one relationship between