What is the notation for a lifeline?

What is the notation for a lifeline?

• A. Rectangle with a dashed line attached to it, flowing down the sequence diagram
• B. Circle with a solid line
• C. Rectangle with a solid line only
• D. Diamond shape with a dashed line

Answer: (A)

In sequence diagrams, a lifeline is shown as a rectangle representing the object, with a dashed line extending downward from it to indicate the passage of time and the ongoing existence of that object. So the notation for a lifeline is a rectangle with a dashed line flowing down the sequence diagram. This dashed line is what communicates that the object persists over time while messages are sent between lifelines. The other visual elements serve different purposes—circles, diamonds, and solid lines align with other diagram constructs or message types, not the ongoing timeline of an object.

In sequence diagrams, a lifeline is shown as a rectangle representing the object, with a dashed line extending downward from it to indicate the passage of time and the ongoing existence of that object. So the notation for a lifeline is a rectangle with a dashed line flowing down the sequence diagram. This dashed line is what communicates that the object persists over time while messages are sent between lifelines. The other visual elements serve different purposes—circles, diamonds, and solid lines align with other diagram constructs or message types, not the ongoing timeline of an object.