Which of the following describes the notation used for an execution specification in a sequence diagram?

Which of the following describes the notation used for an execution specification in a sequence diagram?

• A. A thin, vertical rectangle, either white or shaded, that covers a lifeline for the period of time the lifeline is actively executing a behavior
• B. A horizontal dashed line across the lifeline
• C. A rounded box above the lifeline
• D. A diagonal stripe along the lifeline

Answer: (A)

In sequence diagrams, the moment an object is actively performing a behavior is shown with an activation bar, also called an execution specification. This appears as a thin vertical rectangle attached to the lifeline and spans the exact time the object is executing. The rectangle can be white or shaded, but its purpose is to indicate that the lifeline is in an active execution state during that interval. That’s why the described notation fits: a slim vertical rectangle on the lifeline covering the execution period. The other options don’t represent this active execution interval—horizontal dashed lines are typically used for return messages, a rounded box above the lifeline isn’t the standard symbol for execution, and a diagonal stripe along the lifeline isn’t used to denote execution.

In sequence diagrams, the moment an object is actively performing a behavior is shown with an activation bar, also called an execution specification. This appears as a thin vertical rectangle attached to the lifeline and spans the exact time the object is executing. The rectangle can be white or shaded, but its purpose is to indicate that the lifeline is in an active execution state during that interval. That’s why the described notation fits: a slim vertical rectangle on the lifeline covering the execution period. The other options don’t represent this active execution interval—horizontal dashed lines are typically used for return messages, a rounded box above the lifeline isn’t the standard symbol for execution, and a diagonal stripe along the lifeline isn’t used to denote execution.