Sequence Diagram..

Hi friend,
I found particulary interesting that Sequence Diagram are very important in system development. Here is the some information about sequence diagram.
A lifeline in a sequence diagram represents an object and shows all its points of interaction with other objects in events that are important to it. Lifelines start at the top of a sequence diagram and descend vertically to indicate the passage of time. Interactions between objects – messages and replies – are drawn as horizontal direction arrows connecting lifelines. In addition, boxes known as combine fragments are drawn around sets of arrows to mark alternative actions, loops, and other control structures.