Applying UML and Patterns: An Introduction to Object-Oriented Analysis and Design and the Unified Process, Second Edition

27.1. Association Classes

The following domain requirements set the stage for association classes:

• Authorization services assign a merchant ID to each store for identification during communications.

• A payment authorization request from the store to an authorization service needs the merchant ID that identifies the store to the service.

• Furthermore, a store has a different merchant ID for each service.

Where in the UP Domain Model should the merchant ID attribute reside?

Placing merchantID in Store is incorrect because a Store can have more than one value for merchantID. The same is true with placing it in AuthorizationService (see Figure 27.1).

Figure 27.1. Inappropriate use of an attribute.

This leads to the following modeling principle:

In ...