Requirements Engineering

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Requirements Engineering

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2. Topics covered Functional and non-functional requirements Requirements engineering processes Requirements elicitation Requirements specification Requirements validation Requirements
3. Requirements engineering The process of establishing the services that acustomer requires from a system and the
4. What is a requirement? It may range from a high-level abstract statement of a service or
5. Requirements abstraction (Davis) Chapter 4 Requirements Engineering “If a company wishes to let a contract for
6. Types of requirement User requirements Statements in natural language plus diagrams of the services the system
7. User and system requirements Chapter 4 Requirements Engineering 30/10/2014
8. Readers of different types of requirements specification Chapter 4 Requirements Engineering 30/10/2014
9. System stakeholders Any person or organization who is affected by the system in some way and
10. Stakeholders in the Mentcare system Patients whose information is recorded in the system. Doctors who are
11. Stakeholders in the Mentcare system A medical ethics manager who must ensure that the system meets
12. Agile methods and requirements Many agile methods argue that producing detailed system requirements is a waste
13. Functional and non-functional requirements Chapter 4 Requirements Engineering 30/10/2014
14. Functional and non-functional requirements Functional requirements Statements of services the system should provide, how the system
15. Functional requirements Describe functionality or system services. Depend on the type of software, expected users and
16. Mentcare system: functional requirements A user shall be able to search the appointments lists for all
17. Requirements imprecision Problems arise when functional requirements are not precisely stated. Ambiguous requirements may be interpreted
18. Requirements completeness and consistency In principle, requirements should be both complete and consistent. Complete They should
19. Non-functional requirements These define system properties and constraints e.g. reliability, response time and storage requirements. Constraints
20. Types of nonfunctional requirement Chapter 4 Requirements Engineering 30/10/2014
21. Non-functional requirements implementation Non-functional requirements may affect the overall architecture of a system rather than the
22. Non-functional classifications Product requirements Requirements which specify that the delivered product must behave in a particular
23. Examples of nonfunctional requirements in the Mentcare system Chapter 4 Requirements Engineering 30/10/2014
24. Goals and requirements Non-functional requirements may be very difficult to state precisely and imprecise requirements may
25. Usability requirements The system should be easy to use by medical staff and should be organized
26. Metrics for specifying nonfunctional requirements Chapter 4 Requirements Engineering 30/10/2014
27. Requirements engineering processes Chapter 4 Requirements Engineering 30/10/2014
28. Requirements engineering processes The processes used for RE vary widely depending on the application domain, the
29. A spiral view of the requirements engineering process Chapter 4 Requirements Engineering 30/10/2014
30. Requirements elicitation Chapter 4 Requirements Engineering 30/10/2014
31. Requirements elicitation and analysis Sometimes called requirements elicitation or requirements discovery. Involves technical staff working with
32. Requirements elicitation Chapter 4 Requirements Engineering 30/10/2014
33. Requirements elicitation Software engineers work with a range of system stakeholders to find out about the
34. Problems of requirements elicitation Stakeholders don’t know what they really want. Stakeholders express requirements in their
35. The requirements elicitation and analysis process Chapter 4 Requirements Engineering 30/10/2014
36. Process activities Requirements discovery Interacting with stakeholders to discover their requirements. Domain requirements are also discovered
37. Requirements discovery The process of gathering information about the required and existing systems and distilling the
38. Interviewing Formal or informal interviews with stakeholders are part of most RE processes. Types of interview
39. Interviews in practice Normally a mix of closed and open-ended interviewing. Interviews are good for getting
40. Problems with interviews Application specialists may use language to describe their work that isn’t easy for
41. Ethnography A social scientist spends a considerable time observing and analysing how people actually work. People
42. Scope of ethnography Requirements that are derived from the way that people actually work rather than
43. Focused ethnography Developed in a project studying the air traffic control process Combines ethnography with prototyping
44. Ethnography and prototyping for requirements analysis Chapter 4 Requirements Engineering 30/10/2014
45. Stories and scenarios Scenarios and user stories are real-life examples of how a system can be
46. Photo sharing in the classroom (iLearn) Jack is a primary school teacher in Ullapool (a village
47. Scenarios A structured form of user story Scenarios should include A description of the starting situation;
48. Uploading photos iLearn) Initial assumption: A user or a group of users have one or more
49. Uploading photos What can go wrong: No moderator is associated with the selected project. An email
50. Requirements specification Chapter 4 Requirements Engineering 30/10/2014
51. Requirements specification The process of writing donw the user and system requirements in a requirements document.
52. Ways of writing a system requirements specification Chapter 4 Requirements Engineering 30/10/2014
53. Requirements and design In principle, requirements should state what the system should do and the design
54. Natural language specification Requirements are written as natural language sentences supplemented by diagrams and tables. Used
55. Guidelines for writing requirements Invent a standard format and use it for all requirements. Use language
56. Problems with natural language Lack of clarity Precision is difficult without making the document difficult to
57. Example requirements for the insulin pump software system Chapter 4 Requirements Engineering 30/10/2014
58. Structured specifications An approach to writing requirements where the freedom of the requirements writer is limited
59. Form-based specifications Definition of the function or entity. Description of inputs and where they come from.
60. A structured specification of a requirement for an insulin pump Chapter 4 Requirements Engineering 30/10/2014
61. A structured specification of a requirement for an insulin pump Chapter 4 Requirements Engineering 30/10/2014
62. Tabular specification Used to supplement natural language. Particularly useful when you have to define a number
63. Tabular specification of computation for an insulin pump Chapter 4 Requirements Engineering 30/10/2014
64. Use cases Use-cases are a kind of scenario that are included in the UML. Use cases
65. Use cases for the Mentcare system Chapter 4 Requirements Engineering 30/10/2014
66. The software requirements document The software requirements document is the official statement of what is required
67. Users of a requirements document Chapter 4 Requirements Engineering 30/10/2014
68. Requirements document variability Information in requirements document depends on type of system and the approach to
69. The structure of a requirements document Chapter 4 Requirements Engineering 30/10/2014
70. The structure of a requirements document Chapter 4 Requirements Engineering 30/10/2014
71. Requirements validation Chapter 4 Requirements Engineering 30/10/2014
72. Requirements validation Concerned with demonstrating that the requirements define the system that the customer really wants.
73. Requirements checking Validity. Does the system provide the functions which best support the customer’s needs? Consistency.
74. Requirements validation techniques Requirements reviews Systematic manual analysis of the requirements. Prototyping Using an executable model
75. Requirements reviews Regular reviews should be held while the requirements definition is being formulated. Both client
76. Review checks Verifiability Is the requirement realistically testable? Comprehensibility Is the requirement properly understood? Traceability Is
77. Requirements change Chapter 4 Requirements Engineering 30/10/2014
78. Changing requirements The business and technical environment of the system always changes after installation. New hardware
79. Changing requirements Large systems usually have a diverse user community, with many users having different requirements
80. Requirements evolution Chapter 4 Requirements Engineering 30/10/2014
81. Requirements management Requirements management is the process of managing changing requirements during the requirements engineering process
82. Requirements management planning Establishes the level of requirements management detail that is required. Requirements management decisions:
83. Requirements change management Deciding if a requirements change should be accepted Problem analysis and change specification
84. Requirements change management Chapter 4 Requirements Engineering 30/10/2014
85. Key points Requirements for a software system set out what the system should do and define
86. Key points The requirements engineering process is an iterative process that includes requirements elicitation, specification and
87. Key points Requirements specification is the process of formally documenting the user and system requirements and
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Topics covered
Functional and non-functional requirements
Requirements engineering processes
Requirements elicitation
Requirements specification
Requirements validation
Requirements change
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Requirements engineering
The process of establishing the services that acustomer requires from

a system and the constraints under which it operates and is developed.
The system requirements are the descriptions of the system services and constraints that are generated during the requirements engineering process.

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What is a requirement?
It may range from a high-level abstract statement

of a service or of a system constraint to a detailed mathematical functional specification.
This is inevitable as requirements may serve a dual function
May be the basis for a bid for a contract - therefore must be open to interpretation;
May be the basis for the contract itself - therefore must be defined in detail;
Both these statements may be called requirements.

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Requirements abstraction (Davis)
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“If a company wishes to let

a contract for a large software development project, it must define its needs in a sufficiently abstract way that a solution is not pre-defined. The requirements must be written so that several contractors can bid for the contract, offering, perhaps, different ways of meeting the client organization’s needs. Once a contract has been awarded, the contractor must write a system definition for the client in more detail so that the client understands and can validate what the software will do. Both of these documents may be called the requirements document for the system.”

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Types of requirement
User requirements
Statements in natural language plus diagrams of the

services the system provides and its operational constraints. Written for customers.
System requirements
A structured document setting out detailed descriptions of the system’s functions, services and operational constraints. Defines what should be implemented so may be part of a contract between client and contractor.

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User and system requirements
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Readers of different types of requirements specification
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System stakeholders
Any person or organization who is affected by the system

in some way and so who has a legitimate interest
Stakeholder types
End users
System managers
System owners
External stakeholders

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Stakeholders in the Mentcare system
Patients whose information is recorded in the

system.
Doctors who are responsible for assessing and treating patients.
Nurses who coordinate the consultations with doctors and administer some treatments.
Medical receptionists who manage patients’ appointments.
IT staff who are responsible for installing and maintaining the system.

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Stakeholders in the Mentcare system
A medical ethics manager who must ensure

that the system meets current ethical guidelines for patient care.
Health care managers who obtain management information from the system.
Medical records staff who are responsible for ensuring that system information can be maintained and preserved, and that record keeping procedures have been properly implemented.

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Agile methods and requirements
Many agile methods argue that producing detailed system

requirements is a waste of time as requirements change so quickly.
The requirements document is therefore always out of date.
Agile methods usually use incremental requirements engineering and may express requirements as ‘user stories’ (discussed in Chapter 3).
This is practical for business systems but problematic for systems that require pre-delivery analysis (e.g. critical systems) or systems developed by several teams.

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Functional and non-functional requirements
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Functional and non-functional requirements
Functional requirements
Statements of services the system should provide,

how the system should react to particular inputs and how the system should behave in particular situations.
May state what the system should not do.
Non-functional requirements
Constraints on the services or functions offered by the system such as timing constraints, constraints on the development process, standards, etc.
Often apply to the system as a whole rather than individual features or services.
Domain requirements
Constraints on the system from the domain of operation

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Functional requirements
Describe functionality or system services.
Depend on the type of software,

expected users and the type of system where the software is used.
Functional user requirements may be high-level statements of what the system should do.
Functional system requirements should describe the system services in detail.

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Mentcare system: functional requirements
A user shall be able to search the

appointments lists for all clinics.
The system shall generate each day, for each clinic, a list of patients who are expected to attend appointments that day.
Each staff member using the system shall be uniquely identified by his or her 8-digit employee number.

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Requirements imprecision
Problems arise when functional requirements are not precisely stated.
Ambiguous requirements

may be interpreted in different ways by developers and users.
Consider the term ‘search’ in requirement 1
User intention – search for a patient name across all appointments in all clinics;
Developer interpretation – search for a patient name in an individual clinic. User chooses clinic then search.

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Requirements completeness and consistency
In principle, requirements should be both complete and

consistent.
Complete
They should include descriptions of all facilities required.
Consistent
There should be no conflicts or contradictions in the descriptions of the system facilities.
In practice, because of system and environmental complexity, it is impossible to produce a complete and consistent requirements document.

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Non-functional requirements
These define system properties and constraints e.g. reliability, response time

and storage requirements. Constraints are I/O device capability, system representations, etc.
Process requirements may also be specified mandating a particular IDE, programming language or development method.
Non-functional requirements may be more critical than functional requirements. If these are not met, the system may be useless.

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Types of nonfunctional requirement
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Non-functional requirements implementation
Non-functional requirements may affect the overall architecture of a

system rather than the individual components.
For example, to ensure that performance requirements are met, you may have to organize the system to minimize communications between components.
A single non-functional requirement, such as a security requirement, may generate a number of related functional requirements that define system services that are required.
It may also generate requirements that restrict existing requirements.

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Non-functional classifications
Product requirements
Requirements which specify that the delivered product must behave

in a particular way e.g. execution speed, reliability, etc.
Organisational requirements
Requirements which are a consequence of organisational policies and procedures e.g. process standards used, implementation requirements, etc.
External requirements
Requirements which arise from factors which are external to the system and its development process e.g. interoperability requirements, legislative requirements, etc.

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Examples of nonfunctional requirements in the Mentcare system
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Goals and requirements
Non-functional requirements may be very difficult to state precisely

and imprecise requirements may be difficult to verify.
Goal
A general intention of the user such as ease of use.
Verifiable non-functional requirement
A statement using some measure that can be objectively tested.
Goals are helpful to developers as they convey the intentions of the system users.

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Usability requirements
The system should be easy to use by medical staff

and should be organized in such a way that user errors are minimized. (Goal)
Medical staff shall be able to use all the system functions after four hours of training. After this training, the average number of errors made by experienced users shall not exceed two per hour of system use. (Testable non-functional requirement)

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Metrics for specifying nonfunctional requirements
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Requirements engineering processes
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Requirements engineering processes
The processes used for RE vary widely depending on

the application domain, the people involved and the organisation developing the requirements.
However, there are a number of generic activities common to all processes
Requirements elicitation;
Requirements analysis;
Requirements validation;
Requirements management.
In practice, RE is an iterative activity in which these processes are interleaved.

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A spiral view of the requirements engineering process
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Requirements elicitation
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Requirements elicitation and analysis
Sometimes called requirements elicitation or requirements discovery.
Involves technical

staff working with customers to find out about the application domain, the services that the system should provide and the system’s operational constraints.
May involve end-users, managers, engineers involved in maintenance, domain experts, trade unions, etc. These are called stakeholders.

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Requirements elicitation
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Requirements elicitation
Software engineers work with a range of system stakeholders to

find out about the application domain, the services that the system should provide, the required system performance, hardware constraints, other systems, etc.
Stages include:
Requirements discovery,
Requirements classification and organization,
Requirements prioritization and negotiation,
Requirements specification.

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Problems of requirements elicitation
Stakeholders don’t know what they really want.
Stakeholders express

requirements in their own terms.
Different stakeholders may have conflicting requirements.
Organisational and political factors may influence the system requirements.
The requirements change during the analysis process. New stakeholders may emerge and the business environment may change.

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The requirements elicitation and analysis process
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Process activities
Requirements discovery
Interacting with stakeholders to discover their requirements. Domain requirements

are also discovered at this stage.
Requirements classification and organisation
Groups related requirements and organises them into coherent clusters.
Prioritisation and negotiation
Prioritising requirements and resolving requirements conflicts.
Requirements specification
Requirements are documented and input into the next round of the spiral.

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Requirements discovery
The process of gathering information about the required and existing

systems and distilling the user and system requirements from this information.
Interaction is with system stakeholders from managers to external regulators.
Systems normally have a range of stakeholders.

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Interviewing
Formal or informal interviews with stakeholders are part of most RE

processes.
Types of interview
Closed interviews based on pre-determined list of questions
Open interviews where various issues are explored with stakeholders.
Effective interviewing
Be open-minded, avoid pre-conceived ideas about the requirements and are willing to listen to stakeholders.
Prompt the interviewee to get discussions going using a springboard question, a requirements proposal, or by working together on a prototype system.

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Interviews in practice
Normally a mix of closed and open-ended interviewing.
Interviews are

good for getting an overall understanding of what stakeholders do and how they might interact with the system.
Interviewers need to be open-minded without pre-conceived ideas of what the system should do
You need to prompt the use to talk about the system by suggesting requirements rather than simply asking them what they want.

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Problems with interviews
Application specialists may use language to describe their work

that isn’t easy for the requirements engineer to understand.
Interviews are not good for understanding domain requirements
Requirements engineers cannot understand specific domain terminology;
Some domain knowledge is so familiar that people find it hard to articulate or think that it isn’t worth articulating.

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Ethnography
A social scientist spends a considerable time observing and analysing how

people actually work.
People do not have to explain or articulate their work.
Social and organisational factors of importance may be observed.
Ethnographic studies have shown that work is usually richer and more complex than suggested by simple system models.

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Scope of ethnography
Requirements that are derived from the way that people

actually work rather than the way I which process definitions suggest that they ought to work.
Requirements that are derived from cooperation and awareness of other people’s activities.
Awareness of what other people are doing leads to changes in the ways in which we do things.
Ethnography is effective for understanding existing processes but cannot identify new features that should be added to a system.

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Focused ethnography
Developed in a project studying the air traffic control process
Combines

ethnography with prototyping
Prototype development results in unanswered questions which focus the ethnographic analysis.
The problem with ethnography is that it studies existing practices which may have some historical basis which is no longer relevant.

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Ethnography and prototyping for requirements analysis
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Stories and scenarios
Scenarios and user stories are real-life examples of how

a system can be used.
Stories and scenarios are a description of how a system may be used for a particular task.
Because they are based on a practical situation, stakeholders can relate to them and can comment on their situation with respect to the story.

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Photo sharing in the classroom (iLearn)
Jack is a primary school teacher

in Ullapool (a village in northern Scotland). He has decided that a class project should be focused around the fishing industry in the area, looking at the history, development and economic impact of fishing. As part of this, pupils are asked to gather and share reminiscences from relatives, use newspaper archives and collect old photographs related to fishing and fishing communities in the area. Pupils use an iLearn wiki to gather together fishing stories and SCRAN (a history resources site) to access newspaper archives and photographs. However, Jack also needs a photo sharing site as he wants pupils to take and comment on each others’ photos and to upload scans of old photographs that they may have in their families. Jack sends an email to a primary school teachers group, which he is a member of to see if anyone can recommend an appropriate system. Two teachers reply and both suggest that he uses KidsTakePics, a photo sharing site that allows teachers to check and moderate content. As KidsTakePics is not integrated with the iLearn authentication service, he sets up a teacher and a class account. He uses the iLearn setup service to add KidsTakePics to the services seen by the pupils in his class so that when they log in, they can immediately use the system to upload photos from their mobile devices and class computers.

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Scenarios
A structured form of user story
Scenarios should include
A description of the

starting situation;
A description of the normal flow of events;
A description of what can go wrong;
Information about other concurrent activities;
A description of the state when the scenario finishes.

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Uploading photos iLearn)
Initial assumption: A user or a group of users

have one or more digital photographs to be uploaded to the picture sharing site. These are saved on either a tablet or laptop computer. They have successfully logged on to KidsTakePics.
Normal: The user chooses upload photos and they are prompted to select the photos to be uploaded on their computer and to select the project name under which the photos will be stored. They should also be given the option of inputting keywords that should be associated with each uploaded photo. Uploaded photos are named by creating a conjunction of the user name with the filename of the photo on the local computer.
On completion of the upload, the system automatically sends an email to the project moderator asking them to check new content and generates an on-screen message to the user that this has been done.

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Uploading photos
What can go wrong:
No moderator is associated with the

selected project. An email is automatically generated to the school administrator asking them to nominate a project moderator. Users should be informed that there could be a delay in making their photos visible.
Photos with the same name have already been uploaded by the same user. The user should be asked if they wish to re-upload the photos with the same name, rename the photos or cancel the upload. If they chose to re-upload the photos, the originals are overwritten. If they chose to rename the photos, a new name is automatically generated by adding a number to the existing file name.
Other activities: The moderator may be logged on to the system and may approve photos as they are uploaded.
System state on completion: User is logged on. The selected photos have been uploaded and assigned a status ‘awaiting moderation’. Photos are visible to the moderator and to the user who uploaded them.

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Requirements specification
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Requirements specification
The process of writing donw the user and system requirements

in a requirements document.
User requirements have to be understandable by end-users and customers who do not have a technical background.
System requirements are more detailed requirements and may include more technical information.
The requirements may be part of a contract for the system development
It is therefore important that these are as complete as possible.

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Ways of writing a system requirements specification
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Requirements and design
In principle, requirements should state what the system should

do and the design should describe how it does this.
In practice, requirements and design are inseparable
A system architecture may be designed to structure the requirements;
The system may inter-operate with other systems that generate design requirements;
The use of a specific architecture to satisfy non-functional requirements may be a domain requirement.
This may be the consequence of a regulatory requirement.

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Natural language specification
Requirements are written as natural language sentences supplemented by

diagrams and tables.
Used for writing requirements because it is expressive, intuitive and universal. This means that the requirements can be understood by users and customers.

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Guidelines for writing requirements
Invent a standard format and use it for

all requirements.
Use language in a consistent way. Use shall for mandatory requirements, should for desirable requirements.
Use text highlighting to identify key parts of the requirement.
Avoid the use of computer jargon.
Include an explanation (rationale) of why a requirement is necessary.

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Problems with natural language
Lack of clarity
Precision is difficult without making

the document difficult to read.
Requirements confusion
Functional and non-functional requirements tend to be mixed-up.
Requirements amalgamation
Several different requirements may be expressed together.

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Example requirements for the insulin pump software system
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Structured specifications
An approach to writing requirements where the freedom of the

requirements writer is limited and requirements are written in a standard way.
This works well for some types of requirements e.g. requirements for embedded control system but is sometimes too rigid for writing business system requirements.

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Form-based specifications
Definition of the function or entity.
Description of inputs and where

they come from.
Description of outputs and where they go to.
Information about the information needed for the computation and other entities used.
Description of the action to be taken.
Pre and post conditions (if appropriate).
The side effects (if any) of the function.

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A structured specification of a requirement for an insulin pump
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A structured specification of a requirement for an insulin pump
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Tabular specification
Used to supplement natural language.
Particularly useful when you have to

define a number of possible alternative courses of action.
For example, the insulin pump systems bases its computations on the rate of change of blood sugar level and the tabular specification explains how to calculate the insulin requirement for different scenarios.

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Tabular specification of computation for an insulin pump
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Use cases
Use-cases are a kind of scenario that are included in

the UML.
Use cases identify the actors in an interaction and which describe the interaction itself.
A set of use cases should describe all possible interactions with the system.
High-level graphical model supplemented by more detailed tabular description (see Chapter 5).
UML sequence diagrams may be used to add detail to use-cases by showing the sequence of event processing in the system.

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Use cases for the Mentcare system
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The software requirements document
The software requirements document is the official statement

of what is required of the system developers.
Should include both a definition of user requirements and a specification of the system requirements.
It is NOT a design document. As far as possible, it should set of WHAT the system should do rather than HOW it should do it.

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Users of a requirements document
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Requirements document variability
Information in requirements document depends on type of system

and the approach to development used.
Systems developed incrementally will, typically, have less detail in the requirements document.
Requirements documents standards have been designed e.g. IEEE standard. These are mostly applicable to the requirements for large systems engineering projects.

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The structure of a requirements document
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The structure of a requirements document
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Requirements validation
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Requirements validation
Concerned with demonstrating that the requirements define the system that

the customer really wants.
Requirements error costs are high so validation is very important
Fixing a requirements error after delivery may cost up to 100 times the cost of fixing an implementation error.

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Requirements checking
Validity. Does the system provide the functions which best support

the customer’s needs?
Consistency. Are there any requirements conflicts?
Completeness. Are all functions required by the customer included?
Realism. Can the requirements be implemented given available budget and technology
Verifiability. Can the requirements be checked?

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Requirements validation techniques
Requirements reviews
Systematic manual analysis of the requirements.
Prototyping
Using an executable

model of the system to check requirements. Covered in Chapter 2.
Test-case generation
Developing tests for requirements to check testability.

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Requirements reviews
Regular reviews should be held while the requirements definition is

being formulated.
Both client and contractor staff should be involved in reviews.
Reviews may be formal (with completed documents) or informal. Good communications between developers, customers and users can resolve problems at an early stage.

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Review checks
Verifiability
Is the requirement realistically testable?
Comprehensibility
Is the requirement properly understood?
Traceability
Is the

origin of the requirement clearly stated?
Adaptability
Can the requirement be changed without a large impact on other requirements?

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Requirements change
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Changing requirements
The business and technical environment of the system always changes

after installation.
New hardware may be introduced, it may be necessary to interface the system with other systems, business priorities may change (with consequent changes in the system support required), and new legislation and regulations may be introduced that the system must necessarily abide by.
The people who pay for a system and the users of that system are rarely the same people.
System customers impose requirements because of organizational and budgetary constraints. These may conflict with end-user requirements and, after delivery, new features may have to be added for user support if the system is to meet its goals.

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Changing requirements
Large systems usually have a diverse user community, with many

users having different requirements and priorities that may be conflicting or contradictory.
The final system requirements are inevitably a compromise between them and, with experience, it is often discovered that the balance of support given to different users has to be changed.

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Requirements evolution
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Requirements management
Requirements management is the process of managing changing requirements during

the requirements engineering process and system development.
New requirements emerge as a system is being developed and after it has gone into use.
You need to keep track of individual requirements and maintain links between dependent requirements so that you can assess the impact of requirements changes. You need to establish a formal process for making change proposals and linking these to system requirements.

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Requirements management planning
Establishes the level of requirements management detail that is

required.
Requirements management decisions:
Requirements identification Each requirement must be uniquely identified so that it can be cross-referenced with other requirements.
A change management process This is the set of activities that assess the impact and cost of changes. I discuss this process in more detail in the following section.
Traceability policies These policies define the relationships between each requirement and between the requirements and the system design that should be recorded.
Tool support Tools that may be used range from specialist requirements management systems to spreadsheets and simple database systems.

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Requirements change management
Deciding if a requirements change should be accepted
Problem analysis

and change specification
During this stage, the problem or the change proposal is analyzed to check that it is valid. This analysis is fed back to the change requestor who may respond with a more specific requirements change proposal, or decide to withdraw the request.
Change analysis and costing
The effect of the proposed change is assessed using traceability information and general knowledge of the system requirements. Once this analysis is completed, a decision is made whether or not to proceed with the requirements change.
Change implementation
The requirements document and, where necessary, the system design and implementation, are modified. Ideally, the document should be organized so that changes can be easily implemented.

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Requirements change management
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Key points
Requirements for a software system set out what the system

should do and define constraints on its operation and implementation.
Functional requirements are statements of the services that the system must provide or are descriptions of how some computations must be carried out.
Non-functional requirements often constrain the system being developed and the development process being used.
They often relate to the emergent properties of the system and therefore apply to the system as a whole.

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Key points
The requirements engineering process is an iterative process that includes

requirements elicitation, specification and validation.
Requirements elicitation is an iterative process that can be represented as a spiral of activities – requirements discovery, requirements classification and organization, requirements negotiation and requirements documentation.
You can use a range of techniques for requirements elicitation including interviews and ethnography. User stories and scenarios may be used to facilitate discussions.

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Key points
Requirements specification is the process of formally documenting the user

and system requirements and creating a software requirements document.
The software requirements document is an agreed statement of the system requirements. It should be organized so that both system customers and software developers can use it.

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Requirements Engineering

Содержание

Topics coveredFunctional and non-functional requirementsRequirements engineering processesRequirements elicitationRequirements specificationRequirements validationRequirements changeChapter

Requirements engineeringThe process of establishing the services that acustomer requires from

What is a requirement?It may range from a high-level abstract statement

Requirements abstraction (Davis)Chapter 4 Requirements Engineering“If a company wishes to let

Types of requirementUser requirementsStatements in natural language plus diagrams of the

User and system requirements Chapter 4 Requirements Engineering30/10/2014

Readers of different types of requirements specification Chapter 4 Requirements Engineering30/10/2014

System stakeholdersAny person or organization who is affected by the system

Stakeholders in the Mentcare systemPatients whose information is recorded in the

Stakeholders in the Mentcare systemA medical ethics manager who must ensure

Agile methods and requirementsMany agile methods argue that producing detailed system

Functional and non-functional requirementsChapter 4 Requirements Engineering30/10/2014

Functional and non-functional requirementsFunctional requirementsStatements of services the system should provide,

Functional requirementsDescribe functionality or system services.Depend on the type of software,

Mentcare system: functional requirementsA user shall be able to search the

Requirements imprecisionProblems arise when functional requirements are not precisely stated.Ambiguous requirements

Requirements completeness and consistencyIn principle, requirements should be both complete and

Non-functional requirementsThese define system properties and constraints e.g. reliability, response time

Types of nonfunctional requirement Chapter 4 Requirements Engineering30/10/2014

Non-functional requirements implementationNon-functional requirements may affect the overall architecture of a

Non-functional classificationsProduct requirementsRequirements which specify that the delivered product must behave

Examples of nonfunctional requirements in the Mentcare systemChapter 4 Requirements Engineering30/10/2014

Goals and requirementsNon-functional requirements may be very difficult to state precisely

Usability requirementsThe system should be easy to use by medical staff

Metrics for specifying nonfunctional requirementsChapter 4 Requirements Engineering30/10/2014

Requirements engineering processesChapter 4 Requirements Engineering30/10/2014

Requirements engineering processesThe processes used for RE vary widely depending on

A spiral view of the requirements engineering process Chapter 4 Requirements

Requirements elicitationChapter 4 Requirements Engineering30/10/2014

Requirements elicitation and analysisSometimes called requirements elicitation or requirements discovery.Involves technical

Requirements elicitationChapter 4 Requirements Engineering30/10/2014

Requirements elicitationSoftware engineers work with a range of system stakeholders to

Problems of requirements elicitationStakeholders don’t know what they really want.Stakeholders express

The requirements elicitation and analysis process Chapter 4 Requirements Engineering30/10/2014

Process activitiesRequirements discoveryInteracting with stakeholders to discover their requirements. Domain requirements

Requirements discoveryThe process of gathering information about the required and existing

InterviewingFormal or informal interviews with stakeholders are part of most RE

Interviews in practiceNormally a mix of closed and open-ended interviewing.Interviews are

Problems with interviewsApplication specialists may use language to describe their work

EthnographyA social scientist spends a considerable time observing and analysing how

Scope of ethnographyRequirements that are derived from the way that people

Focused ethnographyDeveloped in a project studying the air traffic control processCombines

Ethnography and prototyping for requirements analysis Chapter 4 Requirements Engineering30/10/2014

Stories and scenariosScenarios and user stories are real-life examples of how

Photo sharing in the classroom (iLearn)Jack is a primary school teacher

ScenariosA structured form of user storyScenarios should includeA description of the

Uploading photos iLearn)Initial assumption: A user or a group of users

Uploading photosWhat can go wrong: No moderator is associated with the

Requirements specificationChapter 4 Requirements Engineering30/10/2014

Requirements specificationThe process of writing donw the user and system requirements

Ways of writing a system requirements specification Chapter 4 Requirements Engineering30/10/2014

Requirements and designIn principle, requirements should state what the system should

Natural language specificationRequirements are written as natural language sentences supplemented by

Guidelines for writing requirementsInvent a standard format and use it for

Problems with natural languageLack of clarity Precision is difficult without making

Example requirements for the insulin pump software system Chapter 4 Requirements

Structured specificationsAn approach to writing requirements where the freedom of the

Form-based specificationsDefinition of the function or entity.Description of inputs and where

A structured specification of a requirement for an insulin pump Chapter

A structured specification of a requirement for an insulin pump Chapter

Tabular specificationUsed to supplement natural language.Particularly useful when you have to

Tabular specification of computation for an insulin pump Chapter 4 Requirements

Use casesUse-cases are a kind of scenario that are included in

Use cases for the Mentcare systemChapter 4 Requirements Engineering30/10/2014

The software requirements documentThe software requirements document is the official statement

Users of a requirements document Chapter 4 Requirements Engineering30/10/2014

Requirements document variabilityInformation in requirements document depends on type of system

The structure of a requirements document Chapter 4 Requirements Engineering30/10/2014

The structure of a requirements document Chapter 4 Requirements Engineering30/10/2014

Requirements validationChapter 4 Requirements Engineering30/10/2014

Requirements validationConcerned with demonstrating that the requirements define the system that

Requirements checkingValidity. Does the system provide the functions which best support

Requirements validation techniquesRequirements reviewsSystematic manual analysis of the requirements.PrototypingUsing an executable

Requirements reviewsRegular reviews should be held while the requirements definition is

Topics covered
Functional and non-functional requirements
Requirements engineering processes
Requirements elicitation
Requirements specification
Requirements validation
Requirements change
Chapter

Requirements engineering
The process of establishing the services that acustomer requires from

What is a requirement?
It may range from a high-level abstract statement

Requirements abstraction (Davis)
Chapter 4 Requirements Engineering
“If a company wishes to let

Types of requirement
User requirements
Statements in natural language plus diagrams of the

User and system requirements
Chapter 4 Requirements Engineering
30/10/2014

Readers of different types of requirements specification
Chapter 4 Requirements Engineering
30/10/2014

System stakeholders
Any person or organization who is affected by the system

Stakeholders in the Mentcare system
Patients whose information is recorded in the

Stakeholders in the Mentcare system
A medical ethics manager who must ensure

Agile methods and requirements
Many agile methods argue that producing detailed system

Functional and non-functional requirements
Chapter 4 Requirements Engineering
30/10/2014

Functional and non-functional requirements
Functional requirements
Statements of services the system should provide,

Functional requirements
Describe functionality or system services.
Depend on the type of software,

Mentcare system: functional requirements
A user shall be able to search the

Requirements imprecision
Problems arise when functional requirements are not precisely stated.
Ambiguous requirements

Requirements completeness and consistency
In principle, requirements should be both complete and

Non-functional requirements
These define system properties and constraints e.g. reliability, response time

Types of nonfunctional requirement
Chapter 4 Requirements Engineering
30/10/2014

Non-functional requirements implementation
Non-functional requirements may affect the overall architecture of a

Non-functional classifications
Product requirements
Requirements which specify that the delivered product must behave

Examples of nonfunctional requirements in the Mentcare system
Chapter 4 Requirements Engineering
30/10/2014

Goals and requirements
Non-functional requirements may be very difficult to state precisely

Usability requirements
The system should be easy to use by medical staff

Metrics for specifying nonfunctional requirements
Chapter 4 Requirements Engineering
30/10/2014

Requirements engineering processes
Chapter 4 Requirements Engineering
30/10/2014

Requirements engineering processes
The processes used for RE vary widely depending on

A spiral view of the requirements engineering process
Chapter 4 Requirements

Requirements elicitation
Chapter 4 Requirements Engineering
30/10/2014

Requirements elicitation and analysis
Sometimes called requirements elicitation or requirements discovery.
Involves technical

Requirements elicitation
Chapter 4 Requirements Engineering
30/10/2014

Requirements elicitation
Software engineers work with a range of system stakeholders to

Problems of requirements elicitation
Stakeholders don’t know what they really want.
Stakeholders express

The requirements elicitation and analysis process
Chapter 4 Requirements Engineering
30/10/2014

Process activities
Requirements discovery
Interacting with stakeholders to discover their requirements. Domain requirements

Requirements discovery
The process of gathering information about the required and existing

Interviewing
Formal or informal interviews with stakeholders are part of most RE

Interviews in practice
Normally a mix of closed and open-ended interviewing.
Interviews are

Problems with interviews
Application specialists may use language to describe their work

Ethnography
A social scientist spends a considerable time observing and analysing how

Scope of ethnography
Requirements that are derived from the way that people

Focused ethnography
Developed in a project studying the air traffic control process
Combines

Ethnography and prototyping for requirements analysis
Chapter 4 Requirements Engineering
30/10/2014

Stories and scenarios
Scenarios and user stories are real-life examples of how

Photo sharing in the classroom (iLearn)
Jack is a primary school teacher

Scenarios
A structured form of user story
Scenarios should include
A description of the

Uploading photos iLearn)
Initial assumption: A user or a group of users

Uploading photos
What can go wrong:
No moderator is associated with the

Requirements specification
Chapter 4 Requirements Engineering
30/10/2014

Requirements specification
The process of writing donw the user and system requirements

Ways of writing a system requirements specification
Chapter 4 Requirements Engineering
30/10/2014

Requirements and design
In principle, requirements should state what the system should

Natural language specification
Requirements are written as natural language sentences supplemented by

Guidelines for writing requirements
Invent a standard format and use it for

Problems with natural language
Lack of clarity
Precision is difficult without making

Example requirements for the insulin pump software system
Chapter 4 Requirements

Structured specifications
An approach to writing requirements where the freedom of the

Form-based specifications
Definition of the function or entity.
Description of inputs and where

A structured specification of a requirement for an insulin pump
Chapter

A structured specification of a requirement for an insulin pump
Chapter

Tabular specification
Used to supplement natural language.
Particularly useful when you have to

Tabular specification of computation for an insulin pump
Chapter 4 Requirements

Use cases
Use-cases are a kind of scenario that are included in

Use cases for the Mentcare system
Chapter 4 Requirements Engineering
30/10/2014

The software requirements document
The software requirements document is the official statement

Users of a requirements document
Chapter 4 Requirements Engineering
30/10/2014

Requirements document variability
Information in requirements document depends on type of system

The structure of a requirements document
Chapter 4 Requirements Engineering
30/10/2014

The structure of a requirements document
Chapter 4 Requirements Engineering
30/10/2014

Requirements validation
Chapter 4 Requirements Engineering
30/10/2014

Requirements validation
Concerned with demonstrating that the requirements define the system that

Requirements checking
Validity. Does the system provide the functions which best support

Requirements validation techniques
Requirements reviews
Systematic manual analysis of the requirements.
Prototyping
Using an executable

Requirements reviews
Regular reviews should be held while the requirements definition is