That arrow indicates that this function body of applyTo eventually calls concept.match(essayresponse). A little time after that, you see an arrow emerging from that box. You can see an activation box starting there, indicating the start of the function body of EssayRubric::applyTo. Look, then at the applyTo call from the scorer to the rubric. All that we can say is that if A is drawn below B, than A occurs after B. We can’t say that one inch of vertical space equals some number of seconds. Now, a sequence diagram indicates the flow of time, but it’s not a strict graph. You must show activation boxes if a the body of a called function makes other calls of its own, or if a function has a return arrow.Īctivation boxes are essential to demonstrating cause-and-effect within the model.I.e., how long we are executing its body or executing other function bodies called from it.Īn activation box marks off the time from the start of execution of a function body to when we return from that body to its caller. Sequence diagrams are all about time, so we sometimes need to indicate just how long a function call is active If a function is recursive (calls itself or calls other functions that eventually call it), it can have multiple activations in memory at any given time. This is not specifically a UML term – it’s a common term when discussing function calls in any programming language, and how function calls are implemented in computer architectures. If your domain/analysis model is still valid,ĭiscovering that your model is missing some operations is one of the advantages of doing sequence diagrams.Īn activation of a function is the information associated with a particular call to that function, including all parameters, local variables, etc.Important Sanity Check: If you draw an arrow from one object of type C to an object of type T, and you label that arrow foo, then the class T must have a function named foo listed as one of its member functions. Normally, show these only when they are important to the understanding of a diagram (e.g., they match one of the named objects) Functions can also have return values, shown as an arrow with a dashed line.Or alternatively, a function call made by some code associated with the first object, calling a member function of the second object.Īs with any function calls, these can include parameters. Each solid arrow denotes the passing of a message from one object to another.In essence, we have an anonymous object of a known class. This is still a representation of an object, not of a class, and The colon (:) in front to the remaining name is our cue that So UML allows us to drop the object name:Īs we have done for several of the objects in the diagram above, including the checkbook. Then, if we never actually use that name, we’ve distracted the reader for no good reason. We know that it will be a member of the Checkbook class, but if we actually give it a name, the reader will think that’s something they are supposed to remember. For example, in all of our use-cases so far, there has been only a single checkbook. Quite often, we know we want to discuss an object, but don’t really care to give it a name. In UML, the general form for an object declaration isįor example, chkTrans:Transaction indicates that we have an object named “chkTrans” of type “Transaction”. If it seems confusing to use rectangles for both, there is a consistent way to tell them apart. Note that, unlike in the class relationship diagrams, the rectangles here denote individual objects, not classes. In general, objects are shown as rectangles. Human objects are often indicated by a stick figure.To help understand this, we’ll take this apart, one element at a time, looking at what each one shows us.Ī sequence diagram is composed of a number of columns, each headed by an object. Here is a sequence diagram for our “Score Essay” use-case. Sequence diagrams allow us to demonstrate that our model suffices to represent a use case by mapping the steps of the use-case into specific messages (function calls) from one object to another.Īlthough sequence diagrams can be used to illustrate any interesting collaborations (sequences of related messages) among our objects, we most often draw one sequence diagram for each use case.Our domain or analysis models view the world as objects that interact by exchanging messages. What operations are involved, and on which objects These diagrams attempt to show, for some specific use-case or some common interaction: The syntax for the text describing the object is similar to the attributes in the class diagrams.
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