Inside the frame’s content area the loop’s guard is placed towards the top left corner, on top of a lifeline. You draw a frame, and in the frame’s namebox the text “loop” is placed. The loop combination fragment is very similar in appearance to the option combination fragment. In UML 2, modeling a repeating sequence has been improved with the addition of the loop combination fragment. This is something that is used when you need to model a repetitive sequence. Loops are rather basic and easy to grasp.

If the student’s past due balance does not equal zero, then the sequence skips sending any of the messages in the option combination fragment. We include a guard for the option however, the guard is not a required element. According to the diagram, if a student’s past due balance equals zero, then the addStudent, getCostOfClass, and chargeForClass messages are sent. The image below uses an option combination fragment since a lot of messages have to be sent if the student’s past due balance is equal to zero. An option is usually used to model a simplistic “if then” statement, for example, if there are less than five donuts present on the counter, then make two dozen more. The option combination element or fragment is utilized to model a sequence that will occur provided it is given a certain condition. The word “alt” is placed inside the frame’s name box. As you can see below, will notice that an alternative combination fragment element is drawn using a frame. Alternatives allow the modeling of the “if then else” logic (e.g., if you were to buy three items, then you get 20% off your purchase whereas you get 10% off your purchase). This type of elements is utilized to indicate a mutually exclusive choice that exists between more that one message sequence. These would consist of Alternatives, Options and Loops. In this concluding post, we will take a look at the elements known as Combined Fragments. Lifelines, Messages and Guards) that were related to Sequence Diagrams. As we mentioned in the last post – The Basics and Purpose of Sequence Diagrams ~ Part 1, we did discuss three of the main elements (i.e.

Sequence diagram if then else