9.4. Matching Up Use Cases with Actors

Another important step is to match up use cases with actors. The relationship between actors and use cases is potentially many-to-many, in that the same actor might initiate many different use cases, and a single use case might be relevant to many different actors. By cross-referencing actors with use cases, we ensure the following:

• We didn't identify an actor who, in the final analysis, really has no use for the system after all.

• Conversely, that we didn't specify a use case that nobody really cares about after all.

• And most important of all, it enables each actor to focus on the individual part of the system when they are reviewing the use case diagram to make sure that an important requirement the actor might have hasn't been left out of the model.

For each use case–actor combination, it's useful to determine whether the actor consumes information and/or provides information. Another way to view this aspect of a system is whether actors need write access to the system's information resources (providing) versus having read-only access (consuming).

If the number of actors and/or use cases isn't prohibitive, a simple table such as Table 9-1 can be used to summarize all the preceding.

Table 9.1. A Simple Actor/Use Case Cross-Referencing Technique

Initiating Actor	Student	Faculty	Billing System	Etc.
Use Cases
Register for a course	Provides info	N/A	N/A
Post final grades	Consumes info	Provides info	N/A
Request a transcript	Consumes info	Consumes info	N/A
Determine a student's course load	Consumes info	Consumes info	Consumes info
Etc.