2. Objectives
To describe the principal requirements engineering activities and their
relationships
To introduce techniques for requirements elicitation and analysis
To describe requirements validation and the role of requirements
reviews
To discuss the role of requirements management in support of other
requirements engineering processes
4. 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
Feasibility study (assessing whether the system is useful to the business)
Requirement elicitation and analysis (discovering requirements)
Requirement specification (converting these requirements into some
standard form)
Requirement validation (checking that the requirements actually define the
system that the customer wants)
7. 1. Feasibility Study
A feasibility study decides whether or not the proposed system is
worthwhile.
A short focused study that checks
If the system contributes to organisational objectives;
If the system can be engineered using current technology and within budget;
If the system can be integrated with other systems that are used.
8. Feasibility Study Implementation
Based on information assessment (what is required),
information collection and report writing.
Questions for people in the organisation
What if the system wasn’t implemented?
What are current process problems?
How will the proposed system help?
What will be the integration problems?
Is new technology needed? What skills?
What facilities must be supported by the proposed system?
9. 2. Requirement 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.
10. Problems of Requirements Analysis
Stakeholders don’t know what they really want.
Stakeholders express requirements in their own terms.
Different stakeholders may have conflicting requirements.
The requirements change during the analysis process. New
stakeholders may emerge and the business environment
changes.
11. Requirement Elicitation and Analysis Process
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 documentation
Requirements are documented and input into the next round of
the spiral.
13. 2.1 Requirements Discovery
The process of gathering information about the proposed and existing
systems and distilling the user and system requirements from this
information.
Sources of information include documentation, system stakeholders
and the specifications of similar systems.
14. ATM Stakeholders
Bank customers
Representatives of other banks
Bank managers
Counter staff
Database administrators
Security managers
Marketing department
Hardware and software maintenance engineers
Banking regulators
15. Viewpoints
Viewpoints are a way of structuring the requirements to represent the
perspectives of different stakeholders. Stakeholders may be classified
under different viewpoints.
This multi-perspective analysis is important as there is no single correct
way to analyse system requirements.
16. Types of Viewpoint
Interactor viewpoints
People or other systems that interact directly with the system. In an
ATM, the customer is an interactor VP.
Indirect viewpoints
Stakeholders who do not use the system themselves but who
influence the requirements. In an ATM, management and security
staff are indirect viewpoints.
Domain viewpoints
Domain characteristics and constraints that influence the
requirements. In an ATM, an example would be standards for inter-
bank communications.
17. Viewpoint Identification
Identify viewpoints using
Providers and receivers of system services.
Systems that interact directly with the system being specified.
Regulations and standards.
Sources of business and non-functional requirements.
Engineers who have to develop and maintain the system.
Marketing and other business viewpoints.
19. Interviewing
In formal or informal interviewing, the RE team puts questions to
stakeholders about the system that they use and the system to be
developed.
There are two types of interview
Closed interviews where a pre-defined set of questions are answered.
Open interviews where there is no pre-defined agenda and a range of issues
are explored with stakeholders.
20. 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.
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.
21. Effective interviewers
Interviewers should be open-minded, willing to listen to stakeholders
and should not have pre-conceived ideas about the requirements.
They should prompt the interviewee with a question or a proposal and
should not simply expect them to respond to a question such as ‘what
do you want’.
22. Scenarios
Scenarios are real-life examples of how a system can be used.
They 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.
25. Use cases
Use-cases are a scenario based technique in the UML which 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.
Sequence diagrams may be used to add detail to use-cases by showing the
sequence of event processing in the system.
27. Ethnography
A social scientists 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.
Ethnography is an observational technique that can be
used to understand social and organisation requirements.
Ethnographic studies have shown that work is usually
richer and more complex than suggested by simple system
models.
28. 4. 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.
29. 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?
30. Requirements Validation Techniques
Requirements reviews
Systematic manual analysis of the requirements.
Prototyping
Using an executable model of the system to check requirements.
Test-case generation
Developing tests for requirements to check testability.
31. 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.
32. 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?
33. Requirements Management
Requirements management is the process of managing
changing requirements during the requirements
engineering process and system development.
Requirements are inevitably incomplete and inconsistent
New requirements emerge during the process as business needs
change and a better understanding of the system is developed;
Different viewpoints have different requirements and these are often
contradictory.
34. Requirements Change
The priority of requirements from different viewpoints changes during
the development process.
System customers may specify requirements from a business
perspective that conflict with end-user requirements.
The business and technical environment of the system changes during
its development.
36. Requirements Management Planning
During the requirements engineering process, you have to
plan:
Requirements identification
How requirements are individually identified;
A change management process
The process followed when analysing a requirements change;
Traceability policies
The amount of information about requirements relationships that is
maintained;
CASE tool support
The tool support required to help manage requirements change;
37. Traceability
Traceability is concerned with the relationships between
requirements, their sources and the system design
Source traceability
Links from requirements to stakeholders who proposed these
requirements;
Requirements traceability
Links between dependent requirements;
Design traceability
Links from the requirements to the design;
40. SUMMARY
The requirements engineering process includes a feasibility study,
requirements elicitation and analysis, requirements specification and
requirements management.
Requirements elicitation and analysis is iterative involving domain
understanding, requirements collection, classification, structuring,
prioritisation and validation.
Systems have multiple stakeholders with different requirements.
Social and organisation factors influence system requirements.
Requirements validation is concerned with checks for validity, consistency,
completeness, realism and verifiability.
Business changes inevitably lead to changing requirements.
Requirements management includes planning and change management.
