Use cases are one of the most common techniques applied to document the behavioral requirements for a component-based system. A question that developers often ask is "What information should you include when documenting a use case?" Although some of the sections I suggest here are optional, in my opinion, it is still a good idea to include them. When I am documenting essential use cases (see also the previous tip Modelling essential use cases), I have a tendency to leave out the optional sections (because essential use cases are focused on the what, not the how, and therefore do not need to be as complex as system use cases). When I am documenting system use cases, I typically use all sections. To refresh your memory, the main difference between an essential use case and a system use case is that, in the system use case, you include high-level implementation decisions whereas an essential use case captures the intentions of a user in a technology- and implementation-independent manner.
Two of the sections, actors and included use cases, can actually be determined by simply looking at your use-case diagram. My experience is, however, that it is good to have use cases that can stand on their own -- in other words, use cases that contain all the critical information needed to understand them and the context they are in. This enables your subject matter experts (SMEs) to flesh-out use cases individually. (Perhaps they meet in the mornings to work as a group, and then are assigned use cases to evolve as far as they can on their own in the afternoon, often increasing the productivity of the team.)
- Name. The name should implicitly express the user's intent or purpose of the use case, such as "Enroll Student in Seminar."
- Identifier [Optional]. A unique identifier, such as "UC1701," that can be used in other project artifacts (such as your class model) to refer to the use case.
- Description. Several sentences summarizing the use case.
- Actors [Optional]. The list of actors associated with the use case. Although this information is contained in the use case itself, it helps to increase the understandability of the use case when the diagram is unavailable.
- Status [Optional]. An indication of the status of the use case, typically one of: work in progress, ready for review, passed review, or failed review.
- Frequency. How often this use case is invoked by the actor. This is often a free-form answer such as once per each user login or once per month.
- Preconditions. A list of the conditions, if any, that must be met before a use case may be invoked.
- Postconditions. A list of the conditions, if any, that will be true after the use case finishes successfully.
- Extended use case [Optional]. The use case that this use case extends (if any). An extend association is a generalization relationship where an extending use case continues the behavior of a base use case. The extending use case accomplishes this by inserting additional action sequences into the base use-case sequence. This is modeled using a use-case association with the <<extend>> stereotype.
- Included use cases [Optional]. A list of the use cases this one includes. An include association is a generalization relationship denoting the inclusion of the behavior described by a use case within another use case. This is modeled using a use-case association with the <<include>> stereotype. Also known as a uses or a has-a relationship.
- Assumptions [Optional]. Any important assumptions about the domain that you have made when writing this use case. At some point you should verify these assumptions and evolve them either into decisions (see below) or simply into parts of the basic course or alternate courses of action.
- Basic course of action. The main path of logic an actor follows through a use case. Often referred to as the happy path or the main path because it describes how the use case works when everything works as it normally should.
- Alternate courses of action. The infrequently used paths of logic in a use case, paths that are the result of an alternate way to work, an exception, or an error condition.
- Change history [Optional]. Details about when the use case was modified, why, and by whom.
- Issues [Optional]. A list of issues or action items, if any, that are related to the development of this use case.
- Decisions. A list of critical decisions, typically made by your SMEs, pertaining to the content of the use case. It is important to record these decisions to maintain a group memory.
To make your use case modeling efforts a little easier, I've made a template that reflects the material described in this tip available for download at Ronin International Reusable Templates. The template is in Microsoft Word (and in plain text) format and I hope that you find it, along with the other templates posted at this page, to be of value.
- The earlier tip "Modeling essential use cases"
- Building Object Applications That Work: Your Step-By-Step Handbook for Developing Robust Systems with Object Technology by Scott W. Ambler. New York: Cambridge University Press, 1998.
- Process Patterns -- Building Large-Scale Systems Using Object Technology by Scott Ambler. New York: Cambridge University Press, 1998.
- The Object Primer 2nd Edition by Scott W. Ambler. New York: Cambridge University Press, 2000.
- Software For Use: A Practical Guide to the Models and Methods of Usage-Centered Design by Larry L. Constantine and Lucy A.D.
Lockwood
- Use Case Driven Object Modeling with UML: A Practical Approach by Doug Rosenberg and Kendall Scott
- The Unified Modeling Language Reference Manual by James Rumbaugh, Grady Booch, and Ivar Jacobson. Reading, MA: Addison-Wesley Longman, Inc., 1999.
- Applying Use Cases: A Practical Guide by G. Schneider and J.P. Winters
Scott W. Ambler is President of Ronin International, a consulting firm specializing in object-oriented software process mentoring, architectural modeling, and Enterprise JavaBeans (EJB) development. He has authored or co-authored several books about object-oriented development, including the recently released The Object Primer 2nd Edition, which covers, in detail, the subjects summarized in this article. He can be reached at scott.ambler@ronin-intl.com and at his Web site at www.ambysoft.com.
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