Software Architect's Handbook

Lifeline

In sequence diagrams, an object is graphically represented by a rectangle with its lifeline descending from the center of its bottom:

The lifeline shows the lifespan of the object and is represented by a vertical dashed line. The passage of time starts at the top of the line and goes downward. The rectangle can show both the name of the object and the class, separated by a colon, as follows:

objectname : classname

The object and class names are underlined. A lifeline can represent an object or a class. An object can be left unnamed if we are modeling a class or in cases where the object's name is unimportant. In that situation, you ...