Unit 3

Question 1

What is the difference between verification and validation?

Answer 1

Verification is the set of activities that ensure a solution is being correctly developed, i.e. that it is taking into account the business rules.

Validation ensures that what is being built satisfies the business, i.e. that the business rules implemented are the ones that the business wants.

Question 2

What are the 3 important properties that a representation of business rules should have?

Answer 2

1. Business rules that apply to the whole business should be represented separately from project specific models
2. Business rules should be easy to verify (possibly automatically) and validate
3. Business rules should be represented in a readable language that is easy to verify

Question 3

What are business rules?

Answer 3

Business rules constrain how a business is run and typically include policies, physical lawas, government laws, etc.

Question 4

What are business processes?

Answer 4

Business processes define what is done in a business, by whom, in what order, needing what resources, and with what consequences. They can be modelled using UML activity diagrams.

Question 5

What causes a transition in an activity diagram?

Answer 5

A transition in an activity diagram is caused by the completion of an activity.

Question 6

What is a synchronisation bar, and when is one used in an activity diagram?

Answer 6

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).

Question 7

How does the partitioning of activities into swimlanes help us understand a set of activities?

Answer 7

Swimlanes group activities associated with different roles. The swimlanes show the role that is responsible for each activity.

Question 8

What is the purpose of modelling a workflow in an activity diagram?

Answer 8

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.

Question 9

What is a use case diagram?

Answer 9

A use case diagram in UML is one way to record and communicate your understanding of the use case view of a system.

Question 10

What is the purpose of a system boundary?

Answer 10

The purpose of a system boundary is an optional element used 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.

Question 11

What do actors represent in a use case diagram?

Answer 11

An actor in a use case diagram represents a particular role that an individual might play when interacting with a software system. Actors can also represent other systems, rather than people/roles.

Question 12

What is a precondition?

Answer 12

A precondition is a condition that must hold before an action can be performed.

i.e. What is needed for this operation to be allowed to start?

(b2, p85)

Question 13

What is a postcondition?

Answer 13

A postcondition is a condition that must hold after an action has been performed.

i.e. What will have happened as a result of this operation?

(b2, p85)

Question 14

What is a scenario?

Answer 14

A scenario illustrates one particular way the use case can unfold, by the sequence of interactions the actors have with the system. A scenario is an instance of a use case, similar to an object being an instance of a class.

Question 15

I GASP

What 5 pieces of information should be included in a use case description?

Answer 15

1. A unique identifier for the use case, to allow traceability throughout development
2. The name of the actor that initiates the use case
3. A short description of the goal of the use case
4. A single sequence of steps that describe the main success scenario
5. A textual description of the pre- and postconditions

Question 16

What is the main success scenario?

Answer 16

The main success scenario shows the steps normally followed to achieve the stated goal of the use case, however there can be other scenarios for the same use case, each one having different outcomes depending upon circumstances.

Question 17

What is acceptance testing?

Answer 17

Acceptance testing consists of a series of tests carried out by the customer in conjunction with the developer. These act as a final check that the system does what the customer expects it to.

Question 18

What are the 4 benefits of use cases to the developer?

Answer 18

Use cases help the developer to:

1. Understand the complexity of each use case
2. Determine which actors interact with each use case and to what extent
3. Establish which use cases carry the most risk
4. Estimate how long each use case is likely to take to implement

Question 19

How can use cases be used in an agile approach?

Answer 19

1. Write use cases as needed instead of writing all use cases upfront
2. Write just enough content rather than complete descriptions
3. Write use cases that are useful for communication, rather than heavy ones that are difficult to understand and change

Question 20

What is the purpose of identifying relationships between actors?

Answer 20

The purpose of identifying relationships between actors is to indicate generalisations and establish which use cases can be performed by which actors.

Question 21

What are the two forms of relationship between use cases?

Answer 21

1. Inclusion
   
   • When two or more use cases have an overlapping area of functionality (i.e. a common task) that can be factored out as a distinct use case.
   • The new use case can then be used by each of the original use cases, so avoiding duplication.
   • Inclusion of use cases is always unconditional.
2. Extension
   
   • When a use case has a main success scenario but also alternative scenarios that demand a variation on the original use case - different or additional actions.
   • Each variation can be separated out as a use case that is distrinct from but related to the original use case.
   • An extension is always dependant on the satisfaction of some condition.

Question 22

What are the 2 different ways to reduce the complexity of a use case diagram?

Answer 22

1. Redraw the diagram at a higher level of abstraction
2. Split the diagram up into smaller modules

Question 23

What is a UML stereotype?

Answer 23

A stereotype is a way of attaching extra classifications to a model adding to its basic language.

Question 24

What is the meaning of the << include >> stereotype?

Answer 24

The << include >> stereotype indicates a situation where a use case is reused.

The purpose is to demonstrate commonality between tasks so that reuse can be achieved.

The additional use case is included unconditionally in the original (base) use case.

Question 25

What is the meaning of the << extend >> stereotype?

Answer 25

The << extend >> stereotype indicates a conditional extension to the original use case, known as alternative behaviour. This is used to illustrate a case where there are two or more significantly different scenarios, so that the main case and the additional subsidiary cases are clearly differentiated.

The main purpose of this classification is to separate out a special case.

You should add a condition to each extension (with either a node or an extension point) to specify when the variant behaviour will be included.

Question 26

What problems may arise when developing a software system from a set of use cases?

Answer 26

1. Focus may end up being top-down and function-oriented, resulting in an inflexible and difficult-to-maintain system.
2. Focusing on use cases may cause the developer to sacrifice the object-oriented nature of the system, losing any advantage that UML offers.
3. Design could be mistaken for requirements, where a design decision is mistaken for a constraint.
4. Focusing on the requirements in a use case may cause the developer to view the system too operationally, where a sequence of events is assumed to be the only answer. Developers need to distinguish between requirements and preferred designs.
5. Use cases need to be used in a way that is understandable to the customer but also useful to the developer.

Question 27

What are the 5 tasks involved in preparing a use case model intended for the development team?

Answer 27

1. Define the context for the model by identifying the actors involved in the aspect of the system in question
2. Analyse the behaviour that each actor expects from the proposed system, and identify the use cases (as units of functionality within the overall requirements)
3. Identify the common behaviour that may be reused by other actors, and the variations on common behaviour (the << include >> and << extend >> stereotypes)
4. Draw a model that shows the use cases, the actors and the relationships between them
5. Annotate the use cases as you learn more about the requirements

Question 28

What 3 forms can a prototype take?

Answer 28

1. A mock-up of the human-computer interface for a specific group of users
2. A working version of a subset of the functions required from the eventual product
3. An existing piece of software that has some relevance to the users’ needs and may be considered for further improvement for use in the eventual product

Question 29

What is the main purpose of a prototype?

Answer 29

The main purpose of a prototype is to help with the design of the user interface for the proposed software system and to get users directly involved with the development of the software to minimise or avoid any misunderstandings.

Question 30

What is the main benefits of identifying user interfaces in activity diagrams?

Answer 30

The main benefit of recording user interfaces in an activity diagram is traceability. Also, the developers can identify the relative importance of each user interface for the project plan, particularly when resources are needed for a prototype.