![if statements in sequence diagrams if statements in sequence diagrams](https://schematron.org/image/uml-sequence-diagram-conditional-3.jpg)
Sequence diagram used to surround an entire sequence diagram, if you wish.Īlthough iteration markers and guards can help, they do have weaknesses. You can define parameters and a return value. The frame is drawn to cover the lifelines involved in the Reference refers to an interaction defined on another diagram. Negative the fragment shows an invalid interaction. Loop the fragment may execute multiple times, and the guard indicates the basis of iteration ( Figure 4.4).Ĭritical region the fragment can have only one thread executing it at once. Parallel each fragment is run in parallel. Equivalent to an alt with only one trace ( Figure 4.4). Optional the fragment executes only if the supplied condition is true. Common Operators for Interaction FramesĪlternative multiple fragments only the one whose condition is true will execute ( Figure 4.4). These notations have been dropped from sequence diagrams in UML 2, they are still legal on communication diagrams.
![if statements in sequence diagrams if statements in sequence diagrams](https://www.architexa.com/images/thumbnails/chrono-conditional-collapse.png)
Guards are a conditional expression placed in square brackets and indicate that the message is sent only if the guard is true. You can add some text in square brackets to indicate the basis of the iteration. An iteration marker is a * added to the message name. Figure 4.5 shows some of these unofficial tweaks.įigure 4.5. As a result, you may see diagrams prepared before UML 2 and that use a different approach Īlso, some people don’t like the frames and prefer some of the older conventions. Only the fragment whose guard is true will execute. For conditional logic, you can use an alt operator and put a condition on each fragment. (Table 4.1 lists common operators for interaction frames.) To show a loop, you use the loop operand with a single fragment and put the basis of the iteration in the guard. Each frame hasĪn operator and each fragment may have a guard. In general, frames consist of some region of a sequence diagram that is divided into one or more fragments. Figure 4.4 shows a simple algorithm based on the following pseudocode: Both loops and conditionals use interaction frames, which are ways of marking off a piece of a sequence diagram. Treat sequence diagrams as a visualization of how objects interact rather than If you want to show control structures like this, you are better off with anĪctivity diagram or indeed with code itself. This isn’t what sequence diagrams are good at.
![if statements in sequence diagrams if statements in sequence diagrams](https://i.pinimg.com/originals/8b/3c/84/8b3c840cb740275cb02ed42d4c922aba.jpg)
Note the message and reply going to and from the referenced interaction (Interaction 2) matches up with the message and reply in referencing interaction (Interaction 1).UML Distilled: A Brief Guide to the Standard Object Modeling Language, 3rd EditionĪ common issue with sequence diagrams is how to show looping and conditional behavior. Interaction 1 is referenced inside Interaction 2. For this, we use References that reference other interaction sequence diagrams.įairly simply, you place a frame in the one diagram with the name of the referenced interaction. In other cases, certain parts of your interactions might be derived from others. However, some diagrams might grow considerably large. The interaction sequence diagrams shown above are all fairly small and succinct. A dashed line divides the different conditions. Similar to loops, you bind these messages in a new frame, with the title alt and the different conditions that will result in each path. In Interaction Sequence diagrams, they are alternatives. Just bind the messages that will be looped in a new frame, and remember to name the condition! While the condition is true, all the action within the loop frame will be repeated. They are pretty simple in Interaction Sequence Diagrams. You know what loops are, right? For-loops, while-loops, etc.