Use Cases in UML: How to Write Effective Use Case Specifications

• First, a brief description is written of only the steps required for the normal flow of the use case (i.e., what functionality the use case provides).
• As analysis progresses, these steps are elaborated with more detail.
• Finally, alternative and exception flows are added to the use case.
• Each project can adopt a standard use case template to create use case specifications.

Use Case vs. Use Case Specification

A use case describes a task performed by an actor that delivers business value. A use case can be visualized as a use case diagram and/or a structured textual specification format:

• Interaction — System use cases describe how an actor interacts with the system to achieve a defined business goal.
• Manual — A sequence of actions performed by the actor.
• Automated — A sequence of steps executed by a program or script.

Characteristics of a Use Case

A use case has:

• Only one goal
• One starting point
• One ending point
• Multiple paths from start to finish
  • That is, it specifies behavior for various possible conditions
  • Each condition may require specific actions

For example — Customer Pays a Bill:

There are multiple paths to achieve the goal:

• By phone
• By mail
• In person
• By check
• By cash, etc.

Paths that do not lead to the goal:

• Credit card declined

Agile Use Case Approach

The use case model and its individual use cases evolve incrementally over time. Not all use cases in the model need to be specified at the same level of detail.

Just-in-Time and Just-Enough

Use cases can be written at different levels of detail and scope, each serving a purpose:

• Summary: A general description and high-level overview of a system function or business process.
• User Goal Level: Task-related descriptions of the user’s goals and how they interact with the system; descriptions of specific business processes. User-goal use cases are typically considered to be at the level of the user’s primary work tasks.

Example: Withdrawing cash from an ATM is a useful task and would be a core-level use case, but entering your PIN would not be at this level because it supports the primary task.

• Subfunction: Descriptions of lower-level activities that complete parts of a core use case.

Note: Some use cases may be fully specified to Level II. You stop when you have just enough detail, obtained in a timely and just-enough manner.

Detailed Use Case Specification

A detailed use case is a textual representation that describes a sequence of events along with other relevant use case information in a certain format. People typically adopt a standard use case template to document detailed use case information.

Use Case Template – ATM Cash Withdrawal Example

As mentioned earlier, use cases have various notation styles (e.g., diagrammatic, UML, textual format). Regardless of the notation used, it should be easy to understand. You can use a template such as the one by Alistair Cockburn, or choose the template that best fits your team.

Related Links

1. What is Unified Modeling Language?
2. List of UML Tools
3. Free Trial of Visual Paradigm