Stop   A stop is used to denote that a participant is destroyed during the lifetime represented by the diagram. The lifeline is ended indicating that the participant no longer exists; the dashed line ends in a small cross positioned at the end of the lifeline. A participant may stop itself.

Explanation

Typically many of the participants that are involved in the interaction are not destroyed during the lifetime represented by the diagram. There are circumstances however when a participant is destroyed during the diagram lifetime, and this is explicitly represented. The "X" marks the destruction of the participant and its lifeline ends at this point. The participant cannot partake in any further interactions from that point onward.

Related Entries

Message (Instance Creation)  Paired Element An instance creation is related to an instance destruction as a paired element. A instance can be created during the lifetime of the sequence diagram and can also be destroyed. It is quite common to create an instance use its services and then destroy it again.