Sequence Diagram

                 The sequence diagram is a diagram that shows the interaction between actors and objects in a system and how object communicate with each other in terms of a sequence and show how process operate with one another and in what order. To model different kind of interaction the UML provide a rich syntax for sequence diagram. The sequence diagram show interaction between objects with respect to time sequence. The sequence diagram concern with objects and classes and exchange of massage between objects needed to carry out functionality of the scenario. In the logical view of the system sequence diagrams are associated with use case under the development. The sequence diagram is a construct of a message sequence chart. The sequence diagrams are sometime called event diagrams or event scenarios.

The object and actors involved are listed in the top of the diagram with parallel vertical dot-ted lines drawn vertically from these. The interactions between objects are indicated by annotated arrows. The rectangle on the dotted lines indicates the lifetime of the object. The sequence of interactions between object and actor or between the object themselves (with each other) are read from top to bottom. The annotations on the arrows indicate the calls to objects, their parameters, and the return value.

If the life line of an object it demonstrate a role. The message name written above the horizontal arrows, the message name is an indication of interaction. The synchronous call is represent by solid arrow heads and asynchronous call (messages) is represent by open arrow heads and dashed lines represent reply of a message. If we send a synchronous message it must wait until the massage response and then continue a process. If a caller send an asynchronous message it doesn’t have to wait for a response and it continue processing.

The asynchronous calls are present in a multithreaded application and in a message-oriented middleware. To represent a process are performed in response to the message are represent by a opaque rectangle, the activation boxes, the method call boxes on the top of a life lines. When an object is destroyed, X is drawn on top of the life line, and drawn dashed line below it, it should be a result of message from the object itself or another object. A message originating from a border of the sequence diagram is a message sent from outside the diagram.

Using sequence diagram for code generation or detailed documentation then don’t have to include every interaction in the diagram.

Here is the diagram of sequence diagrams:-

 Sequence diagram for view patient information

This diagram model the interaction between objects involved in the view patient information use case and medical receptionist can see some patient information.