Agent Lifeline

The agent lifeline defines the time period when an agent exists.
An agent lifeline is shown as a vertical dashed line.
Lifelines can be split to show AND/OR parallelism:
- AND parallelism starts at a horizontal heavy bar.
- OR parallelism (inclusive-or) starts at a horizontal heavy bar with a non-filled diamond, and,
- decision (exclusive-or) starts at a horizontal heavy bar with a non-filled diamond with "x" inside the diamond and is continued with a set of parallel vertical lifelines connected to the heavy bar.