In principle, only the method calls are shown in the sequence diagram. This name can be added to the parameters list in parentheses. The method name is placed on this symbol. When an object calls a method of another object, this is symbolized by a continuous arrow which points to the object from which the method was called. If an object calls its own method, the Lifeline thickens again. If an object is involved in a method call, it is active. For objects which are re-created within the program section, the symbol is drawn at the level of the method call in the course of which the object was created. For objects which already exist at the start of the program section, the object symbols are drawn on the upper sheet edge. An object’s lifeline grows in the direction of the lower sheet edge. Objects are shown along the upper sheet edge.Įvery object is on a vertical line - the Lifeline. Classes are not displayed in this diagram. Underlining of the name may be omitted so that no confusion with the class name can occur. Program flow is not always triggered by an object outside of the concerned area, so that in this case no system limit must be set.Īn object is shown by a rectangle containing the name. It usually serves as the start point of the triggering method call. The System Border isolates the concerned part of the program from the rest of the program. The following table contains the sequence diagram symbols. The destruction of an object is represented by a cross on the Lifeline. by calling the method "new"), then the Lifeline of this object begins at this position. If an object is created via the setting of a message (e.g. "arguments" is a comma-separated list of parameter values transferred to the message.
The sending of a signal is always as asynchronous character. "name" is the name of the message to be called, or the name of the signal to be sent.The attribute allocation is only used in synchronous messages with return value. "attribute" can be a local variable of the interaction, or an Element of a Lifeline.The message is noted on the message arrow with the following syntax:
Repeated message sending is modeled by adding the * symbol, in which case the message has the * symbol placed in front. 54: Notation Forms of the various Message Types The Lifeline which belongs to the Element starts first on this place in the diagram e.g., the arrow points to the Lifeline header.įig. A message which creates a new Element is represented by a line and open arrow point.When a message is found the receiver is recognized, but not the sender. Found Message s have an open arrow point.When a message is lost the sender is recognized, but not the receiver. Lost Message s have an open arrow point in the direction of a filled circle.There is accordingly no answer arrow to asynchronous calls. Asynchronous means that the caller does not wait, but rather proceeds immediately after the call. Asynchronous Messages have an open arrow point.The Reply Message to a synchronous call is represented by a dashed line and open arrow point. Synchronous means that the caller waits until the called behavior has ended. Synchronous Message s are represented by filled arrowheads.In the following illustration, the various message types and corresponding notation forms are shown. UML recognizes various types of messages which are demonstrated using various kinds of arrow notation.
Labeling of messages is carried out using the names of the corresponding operations. The transfer of a message is noted using arrows. Put more simply, the sending and receiving of messages determines the start and end of the ExecutionOccurence. Start and End of ExecutionOccurence are defined via the so-called Event Occurrence. These rectangles represent the so-called ExecutionOccurence. This is shown by the elongated rectangle on the Lifeline. When messages are exchanged between Lifelines, a Behavior must also be implemented in the associated elements. In the heading of the Lifeline is the (optional) element name with the associated class in the usual declaration notation: name : type. It is important that the entire diagram represents an interaction, and that an interaction is not only a single message exchange.įig. The sequence diagram in the following illustration shows an interaction among three objects.
The chronological progress of messages is thereby highlighted. Messages are shown using arrows between the Lifelines. The participating objects are represented by a rectangle and a dashed vertical line. When an object is created, and when and to what object information is sent, are all determined here. The messaging sequence corresponds to its horizontal position in the diagram. A Sequence Diagram is primarily concerned with the chronological progression of messages.
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