What is an IF ELSE sequence?

Use the IF-THEN-ELSE sequence to define a condition, test the truth of that condition, and initiate an action based on the test results. Do not code THEN and ELSE on the same logical line. The THEN action is invoked if the logical expression is true. …

How do you use an ALT in a sequence diagram?

alt is used to describe alternative scenarios of a workflow. Only one of the options will be executed. opt is used to describe optional step in workflow. For example, for online shop purchase sequence diagram you may use opt to describe how user can add gift wrapping if she wishes.

How do you represent objects in a sequence diagram?

In the UML, an object in a sequence diagram is drawn as a rectangle containing the name of the object, underlined. An object can be named in one of three ways: the object name, the object name and its class, or just the class name (anonymous object). The three ways of naming an object are shown in Figure below.

How do you represent an exception in sequence diagram?

UML provides neither notation to model exception handling in sequence diagrams nor any reasoning why it is absent. Some clumsy approaches to model try-catch blocks are by utilizing combined fragments – alt (alternatives) and breaks, while adding stereotypes for reply messages representing thrown exceptions.

What is the use of system sequence diagram?

Sequence diagrams are used to express interactions of external elements with the system realizing a use case, interesting specific interactions among elements within the system design, or specify test cases using the UML Testing Profile [2].

What is Alt frame in sequence diagram?

An alternative combined fragment is used to specify an area of a group of lifelines/ actors to show conditional flow in a sequence diagram. It also models the if-then-else logic in the sequence diagram.

How do you show iteration in a sequence diagram?

Below are the steps on how to represent a loop:

1. Create a sequence diagram.
2. Place two objects on the sequence diagram.
3. Draw a message from one object to the other.
4. Draw a note over the message and add a description (for example, “Messages 2 through 4 are repeated.”)