Block 1 Unit 3 Flashcards
What are the important properties that a representation of business rules should have?
The important properties are as follows:
Business rules that apply to the whole business should be represented separately from project specific models.
They should be easy to verify (possibly automatically) and validate.
They should be represented in a readable language that is easy to verify.
Consider whether business rules can be modelled in UML; discuss the consequences in the light of the properties in your answer to (a).
UML can support the specification of business rules either as annotations to the models or in a more formal way through Object Constraint Language (OCL). However UML and OCL do not provide a separate explicit notation for business rules. As a consequence, it does not:
facilitate documentation of the rules independently of other models
facilitate their analysis, validation and change
facilitate their traceability from the business needs to the software solution.
What causes a transition in an activity diagram?
A transition in an activity diagram is caused by the completion of an activity.
What is a synchronisation bar, and when is one used in an activity diagram?
A synchronisation bar is used to mark the point when two or more activities can take place concurrently (a fork) or when a number of concurrent tasks must finish before continuing to the next activity (a join).
Figure 1 represents a particular way of making a cup of coffee. Suggest a reason why the activity add coffee has been placed before the joining synchronisation bar rather than immediately after the bar.
When the kettle is full and you are waiting for the water to boil, there is some time that you can use to add coffee to the cup. Placing the activity ‘add coffee’ after the joining synchronisation bar rather than before it would mean that you would have to wait to carry out the activity until the water had boiled, and the overall time taken for the task would be longer than for the activity diagram shown in Figure 1.
How does the partitioning of activities into swimlanes help us understand a set of activities?
Swimlanes group activities associated with different roles. The swimlanes show the role that is responsible for each activity.
Give one reason for modelling a workflow in an activity diagram.
Activity diagrams represent the sequence of activities. When you are modelling a workflow that involves more than one role, it is possible to identify which role is responsible for a particular activity. An activity diagram can help identify the stages at which each role requires some interaction with the process.
Name two aspects of software development where use case modelling can help.
So far we have encountered these two: eliciting requirements; representing requirements. Later in the module we will also discuss planning iterations of development and validating software systems.
Suggest a reason why use case diagrams are an aid to communication between user and developer.
Use cases offer users an opportunity to understand the system since the use case notation is relatively simple and doesn’t require an understanding of UML. This provides a mechanism that enables developer and client to share a common understanding of the system, as long as the developer provides some text to demonstrate their understanding of the problem.
What is the purpose of a system boundary? Is it always necessary to draw one in a use case diagram?
The purpose of a system boundary is to identify a single system, distinguishing between the internal and external components. Typically, the external components are the actors and the internal components are the use cases. UML says that the system boundary is optional.
Explain why the actors in a use case diagram do not represent actual individuals.
An actor in a use case diagram represents a particular role that an individual might play when interacting with a software system. For example, a receptionist checks guests into and out of a hotel (see Figure 10). But it could be that the person who works as a receptionist at one hotel becomes a guest at another hotel in the chain and hence takes on another role. Actors can also represent other systems, rather than people/roles.
Suggest a guideline that will help you decide whether or not to include an interaction with an external system on your use case diagram.
One possible guideline would be to show interaction with an external system if the use case needs to communicate with the actors that represent the external system.
Are roles in business process models the same as actors in use cases?
Roles in business process models may not correspond directly to actors in use cases as although they interact with a business process they may not interact with a proposed system. Some roles may become irrelevant when introducing a new system or may not need to interact with the system.
What is the relationship between a use case and a scenario? Give examples to illustrate your answer.
For each use case there is a set of possible scenarios. A scenario is an instance of a use case. A scenario describes a sequence of interactions between the system and some actors.
Here are two examples of scenarios. A member of a lending library wishes to borrow a book, and is allowed to do that as long as they have no outstanding loans. Another member wishes to borrow a book, but has exceeded the quota for the number of books that can be borrowed. In each scenario the member wishes to borrow a book, but both the circumstances and outcomes of events are different in each instance. So a use case includes a complex set of requirements that the system must meet in order to cope with every eventuality.
What is meant by a main success scenario?
The main success scenario shows the steps normally followed to achieve the stated goal of the use case. But there can be other scenarios for the same use case, each one having different outcomes depending upon circumstances.
