What is the notation of an asynchronous message in a sequence diagram?

• A. Solid line with open arrowhead
• B. Solid line with filled arrowhead
• C. Dashed line with open arrowhead
• D. Dashed line with filled arrowhead

Answer: (A)

In sequence diagrams, the style of the line and the arrowhead indicate whether the sender waits for a response. An asynchronous message is shown as a dashed line with a hollow (open) arrowhead, signaling that the sender continues without blocking for a reply. If the message were synchronous, it would be a solid line with a filled arrowhead, representing a blocking call. So the notation for an asynchronous message is a dashed line with an open arrowhead.