Block 1 unit 2

Question 1

Where and when does the requirements engineering process take place in an iterative and incremental development process?

Answer 1

The main output of a requirements engineering process is the contract between those commissioning the system and the developers of the system. It has therefore to take place early in the software development process. However, an iterative and incremental process recognises that requirements are not stable and revisiting, clarifying and specifying requirements occur in parallel with the other phases of development.

Question 2

Identify the stakeholders for a system to book appointments for a hospital.

Answer 2

Hospital administrators, receptionists, doctors, nurses, patients, general public.

Question 3

Suggest ways in which requirements may evolve.

Answer 3

Examples are:
◦ new requirements may be added
◦ existing requirements may change because of changes in the environment or in the organisation
◦ some requirements may become obsolete
◦ technologies may evolve
◦ other systems may emerge that introduce interoperability requirements
◦ regulations may change

Question 4

Consider the following list of poorly expressed requirements, indicate which properties are not respected and ask questions to clarify their
meaning:
(a) The software system should provide acceptable performance under maximum load conditions.
(b) If the system fails in operation there should be minimal loss of data.
(c) The software should be developed so that it can be used by inexperienced users

Answer 4

(a) The requirement is ambiguous and not verifiable. How can performance be measured? What is maximum load?
(b) The requirement is ambiguous and not verifiable. What is minimal loss of data?
(c) The requirement is ambiguous. What are the usability criteria?

Question 5

(a) What are requirements and stakeholders and how do they relate to each other?

Answer 5

Requirements are the functions and qualities that are wanted of a product. Stakeholders are the people and organisations with a vested interest in the product. Requirements arise from stakeholders’ needs

Question 6

What are the benefits of documenting requirements within a project?

Answer 6

Requirements record decisions. They are the main reference for what should be built and the basis for validation of the built system. Therefore they need to be documented so that they can be used throughout development.

Question 7

What is an agile approach to requirements engineering documentation?

Answer 7

In an agile approach, requirements documentation serves a purpose and should be done only to the extent that it contributes to that purpose. It should serve as a vehicle for common understanding, communication and
future traceability.

Question 8

Which other activities will be taking place in parallel with requirements engineering?

Answer 8

The definition of the system architecture and an elaboration of tests for the requirements. When defining requirements there are implications for the architecture of the system and each requirement will be related to some test of the final system.

Question 9

Who are the stakeholders in a hotel reservation system?

Answer 9

The hotel owners, receptionists, existing customers, the general public accessing the system to make a reservation.

Question 10

Consider the example of a hotel reservation system and invent some examples of the main inputs for a requirements engineering process.

Answer 10

Examples include:
◦ stakeholder needs – there should be a help system for first-time users of the system
◦ domain information – rooms are identified by a number where the first digit indicates the floor and the subsequent digits indicate the number of the room in a floor
◦ existing documentation – the manual system used for reservations
◦ regulations and organisational standards – an acknowledgement is sent to every customer who makes a reservation.

Question 11

What are the purposes of requirements?

Answer 11

Communication – from the requirements engineer to the designer. As a contract with the client (and other stakeholders) for what the system must do.

Question 12

What is a functional requirement?

Answer 12

A functional requirement describes an action that the product must take if it is to carry out the work it is intended to do.

Question 13

Indicate one property that a functional requirement should not possess?

Answer 13

A functional requirement should not be a statement about a general property such as usability, reliability or maintainability. A functional requirement should not be about the implementation of a solution.

Question 14

What is a non-functional requirement?

Answer 14

A non-functional requirement is a requirement about a quality that the product must have.

Question 15

What are a technical solution requirement and a business functional requirement? Why is it useful to distinguish them?

Answer 15

A technical solution requirement is a constraint on the product resulting from the technology of the solution that must be adopted. Business functional requirements are a specification of the work,or business, independent of the way that work will be carried out. The two types of requirement therefore arise from different domains –
the business domain and the solution domain. It is important to keep issues related to the business separate from those of the solution.

Question 16

What overarching property should the set of functional requirements that result from a requirements-gathering process possess?

Answer 16

The set of functional requirements must fully describe the actions that the intended product should perform. That is, the product’s builder must be able to construct the product desired by the client from the descriptions contained in the functional requirements.

Question 17

How do business events and use cases help in determining functional requirements?

Answer 17

One way to discover the requirements of a system is to use the steps in use case scenarios. Use cases are derived from business events and each use case is described by a set of scenarios. Each step in a scenario details a functional task. All the functional requirements
associated with a use case can be collected from these tasks.

Question 18

How do user stories help in determining functional requirements?

Answer 18

User stories are written by the people who will get some value out of the system and therefore highlight elements of functionality relevant to them. User stories encourage communication and involvement of users and customers with the development process, allowing for change and discovery of requirements throughout.

Question 19

How do you discover whether or not a set of functional requirements is sufficient for the product to be useful and whether the functionality is correct?

Answer 19

Ask the user.

Question 20

Why must functional requirements be testable?

Answer 20

So that it is possible to determine whether the delivered product meets the intention of the user.

Question 21

Can you think of some generic questions to ask that can help in making requirements precise and complete?

Answer 21

Questions of the form ‘when should something happen?’ and ‘to whom should something be sent?’ are useful. You may have thought of others.

Question 22

What is the major problem with a requirement that is written in a natural language such as English?

Answer 22

Ambiguity.

Question 23

Is it possible or desirable to avoid ambiguity entirely in a

requirements specification? What steps can you take to reduce ambiguity in a requirements specification?

Answer 23

It might be possible to avoid ambiguity entirely, but the cost of being so precise can be enormous and the result unreadable. To avoid ambiguity attention has to be given to the language used to represent requirements.

Question 24

Why record the meaning of business and technical words in a requirements specification?

Answer 24

To avoid ambiguity and aid clarity in the usage of terms.

Question 25

Summarise the overall process (based on use cases) described in this section for determining a set of functional requirements.

Answer 25

(a) Understand the domain and determine the business processes and business events.
(b) Determine the scope of the new system and which business events are relevant.
(c) Draw up a set of use cases for the product associated with those events.
(d) Describe each use case by one or more scenarios – a set of steps.
(e) Work through each step of each scenario to determine a set of system requirements.
(f) Check for similar requirements from different use cases.
(g) Search out and remove ambiguity.

Question 26

Describe a process for capturing a set of functional requirements based on user stories.

Answer 26

A requirements capture process based on user stories usually starts with a brainstorming workshop with users and customers to generate an initial set of stories. A story is recorded on a card and triggers a conversation which
helps with understanding the detail, and outline tests for each story. Stories are prioritised, grouped and allocated to an iteration. The outcome of an iteration is validated against its user stories

Question 27

Here is a list of requirements that apply to a product X. For each requirement say whether it is a functional or non-functional requirement and, if it is a functional requirement, whether it is a business requirement or a technical solution requirement.
. X must check a user’s identity
. X must check a user’s password
. X must produce a statement of the user’s account
. X must validate the user’s identity and password within three seconds
. X must be usable by users with limited dexterity
. X must employ the company’s proprietary password maintenance system
. X must operate in arctic climates.

Answer 27

X must check a user’s identity - functional, business requirement (the requirement states what needs to be done, not how to do it)
X must check a user’s password - functional, technical solution requirement (access to the system can be achieved in many ways – passwords are just one mechanism, biometrics may be more appropriate to
this product)
X must produce a statement of the user’s account - functional, business requirement (the requirement states
what needs to be done, not how to do it)
X must validate the user’s identity and password within
three seconds - non-functional
X must be usable by users with limited dexterity - non-functional
X must employ the company’s proprietary password
maintenance system - functional, technical solution requirement (a specific technology is mandated)
X must operate in arctic climates - non-functional

Question 28

Derive some functional requirements for the step of a scenario in a hotel management system stated as, ‘The system shall allocate an available cleaner to each occupied room’. Confine yourself to what must be done, not how it is
to be done.

Answer 28

Here are some suggestions:
. the system shall identify occupied rooms
. the system shall identify available cleaners
. the system shall allocate occupied rooms among the available cleaners while balancing their workloads

Question 29

Imagine that you have been commissioned to produce a requirements recording tool. The purpose of the tool is to allow a requirements analyst to record information about each requirement for a product. An important requirement for the tool is that it should give its users the impression that they are dealing with a stack of cards, each recording a requirement. Without considering the detail of the information to be kept about each
requirement, identify four functional requirements for managing a collection of such records. That is, what would you want the tool to do that would help
you record the requirements you have elicited so far and maintain those requirements as you learn more about the required product? If the tool is to be used on different projects what additional functionality should it possess?

Answer 29

Here are some of the functional requirements that relate to the management of a set of requirements. Yours may differ.
. the product shall enable a new requirement to be entered
. the user shall be able to view each requirement in the set
. the product shall enable a user to amend (edit) an individual requirement
. the product shall enable the user to delete a selected requirement from the set of requirements
. the product shall enable the user to view the summary of all requirements
. the product shall show all requirements that conflict with each requirement
. the product shall perform a range of checks on the set of requirements
. the user shall be able to view all requirements satisfying given criteria
. the product shall show a list of all requirements associated with a selected business event
. the product shall enable the user to create and amend a set of requirements for a new product.

Question 30

From the following list of user stories indicate which ones are good stories and why.

(a) As a user I can select the language for the pages of the website because I am not a native speaker.
(b) As a user I can learn how to use the system easily so that I do not spend too much time.
(c) As a chief information officer (CIO) I want the software to be written in C++.
(d) As a user I want to be able to run the system on an Android phone.

Answer 30

As a user I can select the language for the pages of the website because I am
not a native speaker - Good, but may be too small
As a user I can learn how to use the system easily so that I do not spend too much time - Not a good story because it is not measurable
As a CIO I want the software to be written in C++
Not a good story because it is a constraint on development. It could be a good story if the users were
programmers wanting some library to be developed, or if there was a good reason for it. (Notice that the reason part of the story is missing in ‘as a [role] I want [feature] so that [reason]’.)
As a user I want to be able to run the system on an Android phone - Good story. Notice that you can write a
user story for a non-functional requirement

Question 31

What does the phrase ‘look and feel’ refer to?

Answer 31

Look-and-feel requirements describe the overall appearance of the product to its users.

Question 32

When identifying non-functional requirements for the look and feel of a product, why should you avoid the temptation to provide a design for the user interface?

Answer 32

The production of a design is the task of the product’s designers, once they know the requirements. The look-and-feel requirements are not about the specifics of the user interface.

Question 33

The description of a look-and-feel requirement is often loosely worded and therefore difficult to turn into a good design. What should be done to rectify this situation?

Answer 33

Fit criteria (dealt with in detail in Section 5) should be added to the requirements in order to make each one measurable.

Question 34

What general characteristics should the look and feel of a consumer product have?

Answer 34

The look and feel is concerned with the impression you wish to make. You want it to reflect the distinctive values, ethos and style of your organisation.

Question 35

What do usability and humanity requirements describe?

Answer 35

They describe how easy to use the product should be for its intended users under specified circumstances, and how satisfied they are with it. This includes how easy it is to learn to use the product.

Question 36

What are the effects of usability and humanity on a product?

Answer 36

Usability and humanity impacts on productivity, error rates, stress levels and acceptance. It determines how well the human part of the system can perform.

Question 37

How might you express a usability and humanity requirement more precisely than simply ‘easy to learn’?

Answer 37

A usability and humanity requirement can be expressed more precisely by describing the level of achievement required after the required training or learning period

Question 38

What are the main kinds of performance requirements?

Answer 38

Normally the main performance requirements involve speed (the time to do something), capacity, safety, accuracy, reliability and availability.

Question 39

Rather than accept requirements that state that something should be done speedily and/or efficiently, what should you aim for?

Answer 39

You should look for requirements that specify the speed and efficiency in ways that can be measured objectively. Take into account the possible effects of throughput and volume.

Question 40

What are the problems of specifying performance requirements for web-based systems?

Answer 40

It is hard to specify performance of web-based systems because there are too many unknowns, for example the speed of connection.

Question 41

How do operational requirements differ from performance requirements?

Answer 41

Operational and environmental requirements describe the operational environment (factors external to the product) in which the product must function correctly, whereas performance requirements deal with issues such as speed and size (factors internal to the product).

Question 42

When do cultural requirements usually arise?

Answer 42

Cultural requirements usually arise when:

i. the aim is to sell a product in a different country, particularly a country with a different culture and language from the one that the product was initially designed for
ii. eliciting requirements in an organisation different from one’s own.

Question 43

What is the best approach to dealing with cultural issues?

Answer 43

Obtain the help of stakeholders from that culture.

Question 44

Why are cultural requirements often difficult to deal with?

Answer 44

Cultural and political requirements often involve having to ask personal questions and can be difficult to quantify. Such questioning is likely to be sensitive.

Question 45

What is the most pressing reason for considering legal requirements?

Answer 45

The cost of litigation is a risk for commercial software and can be expensive for other software. There are penalties for non-conformance with the law – fines, imprisonment, and loss of reputation.

Question 46

How should you determine the appropriate law that affects the product?

Answer 46

Obtain help from the company’s lawyers.

Question 47

In the context of a computer system, what is meant by security?

Answer 47

Security is about the prevention of unauthorised access to the system.

Question 48

There are two problem areas for a distributed computing system that go beyond the normal security requirements. What are they?

Answer 48

The additional security problems that arise with a distributed system are:

i. the communication medium is insecure and users’ communications may be intercepted en route and read or altered
ii. on an external network communications will pass through many third-party systems with unknown security measures which cannot be controlled.

Question 49

From the point of view of a security administrator, suggest a useful starting point to monitor potential threats.

Answer 49

One useful focal point is at the boundary of the security domain for which the administrator is responsible. In practice, this is likely to be a firewall for a protected network.

Question 50

What are the five aspects of security from a requirements perspective?

Answer 50

Access, privacy, integrity, audit and immunity.

Question 51

Distinguish between the five aspects of security.

Answer 51

Access – authorised users of data should not be prevented or unnecessarily delayed from accessing that data. This implies that steps should be taken to prevent loss of data and to prevent denial of service attacks.

Privacy – data must not be made available to anyone except authorised users. This implies identification of those who are authorised to access specific items of data.

Integrity – the data held by the system corresponds to the data supplied to the system. Integrity implies that data does not become corrupted.

Audit – the data and functionality of the product can be verified and inappropriate access can be traced.

Immunity – the product is protected against external threats and attacks.

Question 52

What is the first step towards finding whether a solution fits a requirement?

Answer 52

The first step towards finding whether a solution fits a requirement is to attach a quantifiable measure to the requirement so that it is testable.

Question 53

What is a fit criterion?

Answer 53

A fit criterion is a quantification or measurement of a requirement, such that the design solution can be measured to find if it unambiguously meets the requirement.

Question 54

Who needs the fit criteria?

Answer 54

The developers of the product use the fit criteria to develop the product to meet those criteria. The testers use the fit criteria to determine whether the delivered product meets the original requirements. The clients for whom the product is being developed use the fit criteria as acceptance criteria for the product.

Question 55

When are fit criteria specified?

Answer 55

The fit criteria can be written or elicited as the requirements are elicited, for example once use cases have been drawn up and the requirements for each task in each use case have been determined.

Question 56

What is a fit criterion for a functional requirement?

Answer 56

A fit criterion for a functional requirement specifies the completion of the function of the product that is specified by that functional requirement. For example, if the required function is to send an email to a student after a marked TMA has been uploaded by the tutor, then the fit criterion for this requirement is that an email has indeed been sent to the student and reflected in the receiving mailbox.

Question 57

Do the fit criteria of functional requirements have scales of measurement?

Answer 57

No, the fit criteria of functional requirements do not have scales of measurement. Success is tested in terms of a yes/no answer that implies whether the required function is achieved or not.

Question 58

Does a fit criterion indicate how the functional requirement would be tested?

Answer 58

No, a fit criterion provides some target which, when the solution is tested, reveals whether the solution conforms to the requirement. The fit criterion does not indicate how the product will be tested. It merely states that the tester should ensure that the product complies with that fit criterion.

Question 59

What does the fit criterion for a non-functional requirement specify?

Answer 59

A fit criterion for a non-functional requirement specifies a value or values, on a particular scale of measurement, that must be attained by the property or quality that the requirement is concerned with. These values should be realistic, as discussed in the performance requirements example.

Question 60

How might you determine the fit criterion for the performance requirement, ‘The customer services personnel should be able to respond rapidly to customer queries’?

Answer 60

Talking to the users about their own expectations and those of their customers might reveal that the preferred task time is one minute and currently it takes three minutes to answer a customer query because of a cumbersome search facility on the existing system. So the fit criterion for this requirement might be something like, ‘The customer services personnel must be able to find an answer to a customer’s query in not more than one minute of a customer’s call.’

This example shows that the fit criterion is backed by empirical data of the current situation.

Question 61

What is the advantage of capturing requirements using a template rather than adopting your own format?

Answer 61

The template is divided into a fixed set of categories, which means you are less likely to forget some types of requirements. It also saves having to work out what categories of requirements to deal with each time you start a new document. It helps to communicate requirements to other developers because if there is a standard template then everyone will know what information to expect and in what order. It might also allow projects to be compared and even requirements to be reused more easily.