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. The Lifeline which belongs to the Element starts first on this place in the diagram e.g., the arrow points to the Lifeline header. 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 Messages have an open arrow point.When a message is lost the sender is recognized, but not the receiver. Lost Messages 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 Messages 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.
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