# Solutions to Review Questions

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Solutions to Review Questions
Chapter 5 Solutions to Review Questions

5.1 What is the difference between a diagram and a model?
A diagram is a graphical representation of something; a model is an abstraction of some system or subsystem from a particular perspective, using diagrams and textual information.

5.2 What are the two types of UML diagram?
Structural and Behavioural diagrams

5.3 Why do we use models in developping computerized information systems and other artefacts?
A model is quicker and easier to build, it can be used in simulations, it can be used to document the system that we are building and it can represent real or imaginary things from any domain.

5.4 Why do we need standards for the graphical elements of diagrams ?
To promote communication between team members in a project. To communicate over time to other people who will work on the system. To communicate good practice and experience.

5.5 What is the UML notation for each of the following: package, subsystem and model?
See (figure 5.5)

5.6 In what way can we show in UML that something is contained within something else for example a subsystem within another subsystem ? By showing one object contained within the other in the diagram. (See Figure 5.6.)

5.7 What is the notation used for an action in a UML activity diagram?
A rectangle with rounded corners. (See Figure 5.8.) Note that both activities and actions are shown using the same notation, but an activity can be broken down into lower-level activities or actions, whereas actions cannot be broken down any further.

5.8 What links actions in an activity diagram?
Activity edges or control flows.

5.9 In what way can a decision be represented in a UML activity diagram?
By a flow to a diamond shape and then the alternative paths branching out from the diamond. Guard conditions in square brackets are used to show the conditions that must be satisfied for one of the alternatives to be taken. (See Figures 5.9 and 5.11.)

5.10 What is the notation for the two special nodes that start and finish an activity diagram?
The start node (a filled black circle) and the final node (a smaller filled black circle within another circle). (See Figure 5.11.)

5.11 What is meant by a guard condition?
A condition on a flow that must evaluate to ‘true’ for the flow to the next state to take place. (See Figure 5.9.)

5.14 What is the difference between USDP and the Waterfall Lifecycle in the relationship between activities and phases? In the waterfall life cycle, activities and phases are effectively the same, e.g. analysis activities take place in the analysis phase or stage. In an iterative life cycle like the USDP, the same activities represented by workflows take place in each phase, but the balance of activities changes as the life cycle progresses. (See Section 5.4.)

5.12 What is an object flow? An object flow is a flow of data to or from an object when the object is read or updated by an action. If it is updated, then the state of the object may be changed.

5.13 What is the notation for an object flow
An arrow between an object and an action. (See Figure 5.13.)