UML Weekend Crash Course™ - To Parent Directory

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Saturday Afternoon
have currently modeled it. It’s all part of the validation process. Each diagram lends a new
perspective to the information about the system.
A workflow-level Activity diagram represents the order in which a set of Use Cases is executed.
An Activity diagram for one Use Case would explain how the actor interacts with the
system to accomplish the goal of the Use Case, including rules, information exchanged,
decisions made, and work products created.
Modeling the user’s work this way does not bind you to that particular version of the
process. Remember that for each goal (Use Case), there may be any number of valid
processes. But creating such a model will likely reveal the essential elements of the process
in a way that is familiar to the users. The new presentation then facilitates the interview to
clarify the tasks and the reasons behind them. This is your opportunity to ask those allimportant
“why” questions to get at the goal of the process and each task used to perform
the process.
Defining methods
The Activity diagram can also be used to model the implementation of complex methods.
When defining the implementation for an operation, you need to model the sequence of
data manipulation, looping, and decision logic. Modeling complex functions can prevent
problems later when you write the code by revealing all the requirements explicitly in the
diagram. Models make most, if not all, of your assumptions visible and consequently easier
to review and correct.
That last statement is worth emphasizing. It is very tempting to shortcut the
modeling process, but the true value of modeling is in revealing what you
Tip know so that it can be challenged and verified. Making assumptions sabotages
this very valuable benefit of modeling.
The Activity diagram contains all the logical constructs you find in most programming
languages. In fact, it can translate quite well into pseudo-code or even native code.
I should offer one clarification here regarding the vocabulary of the UML. The word operation
in the UML refers to the declaration portion of a behavior defined by a class. This typically
means the name, parameters, and possibly the return type. This is also often called
the interface, the information you use to tell the object what you want it to do.
In contrast, the word method is used to refer to the implementation of an operation, the
code that is executed when you invoke the interface. The Activity diagram may be used to
design the requirements for a method. Because the UML does not provide a place to model
the methods in a Class diagram, or anywhere else, the Activity diagram can fill in this missing
piece.
Tip
Not everyone has accepted or uses the definitions for operation and method
as they are used in the UML.
To be sure, not every operation is complicated enough to warrant drawing an Activity
diagram. The point is that the Activity diagram is well suited to the task when it is needed.