Sequence Diagrams

• Time ordering of flow of control in object interactions for a particular scenario (an instance of a use case);
• Initial objects involved at the top, horizontally (underlined Class names), more important objects to the left;
• Created objects shown horizontally at creation time;
• Objects destroyed indicated by a cross at the time it ceases to exist;
• Sequence of messages between objects shown by horizontal lines (sending and receiving) with arrows;
• Message activation in an object shown by a vertical thin rectangle with a start and finish (Focus of Control);
• Arrows show source and destination of message, and whether synchronous, asynchronous or return;
• Time flows vertically downwards: events flow sequence top to bottom