Use Cases

A use case is a description of a system’s behavior as it responds to a request that originates from outside of that system. The use case technique is used in software and systems engineering to capture the functional requirements of a system. A use case involves a primary actor and a system. Use cases describe the interaction between these two things. An actor is something or someone which exists outside the system under study, and that takes part in a sequence of activities in a dialogue with the system, to achieve some goal. A use case should describe how the system should be used by the actor to achieve a particular goal, include no implementation-specific language, be at the appropriate level of detail, and should not include detail regarding user interfaces and screens. Without a goal a use case is useless.

There are three degrees of detail when writing a use case. First there is a brief use case which consists of a few sentences summarizing the use case. Next is a casual use case which includes a few paragraphs of text summarizing the use case. Then there is a fully dressed use case which is a formal document based on a detailed template with fields for various sections.

A use case can be very beneficial to a business if used right. Some of the benefits include the scope getting understood better, consideration and discussion of alternative paths, organization and structure of the requirements model, making it easy to take a staged delivery approach to projects; test cases can be directly derived from use cases, and effective execution of performance engineering.

Along with benefits, there are limitations when using use cases. Some of these limitations include use case flows are not well suited to easily capturing non-interaction based requirements of a system or non-functional requirements, use case templates do not automatically ensure clarity, use case developers often find it difficult to determine the level of user interface dependency to incorporate in a use case, and use cases can be over-emphasized.

In conclusion, a use case describes a systems behavior as an actor interacts with it. A use case is useless without a goal. There are three types of uses cases and they include a brief use case, a casual use case, and a fully dress use case. Use cases are limiting but are more beneficial.

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