1. Requirements Engineering Process
Chapter 7
Requirements Engineering Process

2. Objectives To describe the principal RE activities.
To introduce techniques for requirements elicitation and analysis.
To describe requirements validation.
To discuss the role of requirements management in support of other RE processes.

3. core, iterative activities
RE processes…
Vary widely depending on:
Application domain
People involved
Organization developing the requirements
Generic activities common to most:
Feasibility study
Requirements elicitation and analysis
Requirements specification
Requirements validation
core, iterative activities

4. RE Process Model

5. Spiral RE Process Model
Emphasizes iterative nature
of core activities

6. Feasibility Study
Feasibility study issues

7. Feasibility study Aims to answer three basic questions:
Would the system contribute to overall organizational objectives?
Could the system be engineered using current technology and within budget?
Could the system be integrated with other systems already in use?

8. Feasibility study issues (a high-level checklist)
How would the organization cope if the system wasn’t implemented?
What are the current process problems and how would the system help with these?
What will the integration problems be?
Is new technology needed? New skills?
What must be supported by the system, and what need not be supported?

9. Elicitation and Analysis
Problems
Process activities
Viewpoint-oriented elicitation
Method-based RE
Interviewing
Scenarios
Social and organizational factors
Ethnography & focused ethnography

10. Elicitation and analysis
Involves working with customers to learn about the application domain, the services needed and the system’s operational constraints, etc.
May also involve end-users, managers, maintenance personnel, domain experts, trade unions, etc. (That is, other stakeholders.)

11. Problems of elicitation and analysis
Getting all, and only, the right people involved
Stakeholders often:
don’t know what they really want
express requirements in their own terms.
have conflicting or competing requirements.
Requirements naturally change as insight improves. (Should this really be thought of as a problem?)
(cont'd)

12. Problems of elicitation and analysis (cont’d)
New stakeholders may emerge.
Political or organizational factors may affect requirements. (Examples?)
The environment may evolve during the RE process.

13. Elicitation and analysis process activities
Requirements discovery
Interacting with stakeholders to discover product and domain requirements
Requirements classification and organization
Grouping and organizing requirements to facilitate analysis
Prioritization and negotiation
Prioritizing requirements and resolving requirements conflicts.
Requirements documentation
Requirements are documented and input into the next round of the spiral.

14. Elicitation and Analysis spiral

15. Viewpoint-oriented elicitation
Stakeholders represent different ways of looking at a problem (“viewpoints”).
A multi-perspective analysis is important as there is no single correct way to analyze system requirements.
Provides a natural way to structure the elicitation process and organize requirements.

16. Types of viewpoints Interactor viewpoints
People or other systems that interact directly with the system.
Indirect viewpoints
Stakeholders who do not use the system themselves but who influence the requirements.
Domain viewpoints
Domain characteristics and constraints that affect the requirements.

17. Suzanne & James Robertson, Atlantic Systems Guild
Method-based RE
“Structured methods” to elicit, analyze, and document requirements.
Examples include:
Ross’ Structured Analysis (SA),
Volere Requirements Process (
Knowledge Aquisition and Sharing for Requirement Engineering (KARE) Esprit project (
Sommerville’s Viewpoint-Oriented Requirements Definition (VORD), and
Thebaut’s Scenario-Based Requirements Engineering (SBRE)
Suzanne & James Robertson, Atlantic Systems Guild
part of “SA/SD”

18. Volere Requirements Process
Start here

19. Volere requirement shell

20. KARE workbench architecture

21. Sommerville’s VORD method

22. VORD standard forms
two points of reference

23. Interviewing
RE’s meet with stakeholders to discuss the system currently in place and the system to be developed.
May be:
formal or informal
closed (with a pre-defined agenda), open (no pre-defined agenda), or a mix
Useful for learning how stakeholders might affect or be affected by the system.
(cont'd)

24. Interviewing (cont’d)
Less useful for learning about domain requirements since:
RE’s may not understand domain-specific terminology;
stakeholders may not communicate such requirements because they are so obvious (to the stakeholders)
Gause & Weinberg (“Exploring Requirements: Quality Before Design,” Dorset House, 1989) describe many useful interviewing techniques.

25. Scenarios Depict examples or scripts of possible system behavior
People often relate to these more readily than to abstract statements of requirements “Give me an example to help tie the parts together” (into a coherent whole.)
Particularly useful in elucidating fragmentary, incomplete, or conflicting requirements

26. Scenario elements
System state at the beginning of the scenario (if relevant)
Sequence of events for a specific case of some generic task the system is required to accomplish.
Any relevant concurrent activities.
System state at the completion of the scenario.

27. A simple scenario
t0: The user enters values for input array A. The values are [1, 23, -4, 7, 19].
t1: The user executes program MAX.
t2: The value of variable BIG is 23 and the values of A are [1, 23, -4, 7, 19].
(Compare this to the interface and operational specification examples from the Chap. 6 lecture notes.)

28. Scenario-Based Requirements Engineering (Thebaut)
A CASE tool supports the rapid construction of an operational specification of the desired system and its environment.
Utilizes a forward chaining, parallel, rule-based language.
An interpreter executes the specification to produce natural language based scenarios of system behavior.

29. Scenario representation in VORD (Sommerville)
VORD supports the graphical description of multi-threaded “event scenarios” to document system behavior:
Data provided and delivered
Control information
Exception processing
The next expected event
Multi-threading supports description of exceptions. (blurs the distinction between scenarios and operational specifications)

30. Scenario for a “start transaction” event
different scenarios
different scenarios

31. UML use-cases and sequence diagrams
Graphical notations for representing abstract scenarios in the UML. (UML is the de facto standard for OO Analysis & Design)
Identify actors in an interaction and describe the interaction itself.
A set of use-cases should describe all types of interactions with the system.
Sequence diagrams show the sequence of event processing.

32. Library use-cases

33. Catalogue management sequence diagram
time

34. Social and organizational factors
All software systems are used in a social and organizational context. This can influence or even dominate system requirements.
Good analysts must be sensitive to these factors, but there is currently no systematic way to tackle their analysis.

35. Example
Consider a system which allows senior manage-ment to access information without going through middle managers.
Managerial status – Senior managers may feel that they are too important to use a keyboard.
Managerial responsibilities – Managers may not have time to learn how to use the system
Organizational resistance – Middle managers who will be made redundant may deliberately provide misleading or incomplete information so the system will fail.

36. Ethnography
A social scientist observes and analyzes how people actually work.
Subjects do not have to explain or otherwise articulate what they do.
Social and organizational factors of importance may be observed.
Ethnographic studies have shown that work is usually richer and more complex than suggested by simple system models.
(Good for studying existing practices, but how will things change when the new system is introduced?)

37. Focused ethnography
Developed during a project studying the air traffic control process.
Combines ethnography with prototyping.
Prototype development raises issues which focus the ethnographic analysis.
Problem with ethnography alone: it studies existing practices which may not be relevant when a new system is put into place.

38. Requirements Validation attributes
techniques

39. Requirements validation
Concerned with whether or not the requirements define a system that the customer really wants. (as opposed to needs?)
Requirements error costs are high, so early validation is very important. (Fixing a requirements error after delivery may cost 100 times that of fixing an error during implementation.)

40. Requirements attributes
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 tested? (More precisely, can the system be tested to determine whether or not the requirements are met?)
(as opposed to wants?)

41. Requirements validation techniques
Requirements reviews / inspections – systematic manual analysis of the requirements.
Prototyping – using an executable model of the system to check requirements. Covered in Chapter 17.
Test-case generation – developing tests for requirements to check testability.
Automated consistency analysis – checking the consistency of a structured requirements description. (CASE – e.g., “Wisdom” tool in KARE workbench)

42. Requirements reviews / inspections
Regular reviews should be held while require-ments are being formulated.
Both client and contractor staff should be involved in reviews. (+ other stakeholders…who?)
Reviews may be formal or informal…
Good communication between developers, customers and users can resolve problems at an early stage.

43. Review check-list Verifiability: Is the requirement testable?
Comprehensibility: Is the requirement understandable?
Traceability: Is the origin of the requirement clearly stated? and rationale!
Adaptability: Can the requirement be changed with minimum impact on other requirements? (Especially when change is anticipated!)

44. Requirements Management Enduring vs. volatile requirements
Planning considerations
Traceability
CASE support
Change management process

45. Requirements management…
…is the process of understanding and controlling requirements change.
Requirements evolve, priorities change, and new requirements emerge as
a better understanding of the system is developed, and
the business and technical environment of the system changes.

46. Enduring and volatile requirements
Enduring requirements: Stable requirements derived from the core activity of the customer organization. (E.g., a hospital will always have doctors, nurses, etc. May be derived from domain models.)
Volatile requirements: Requirements which change during development or when the system is in use. (E.g., requirements derived from the latest health-care policy.)

47. Types of volatile requirements
Mutable – those that change due to changes in the organization’s operating environment.
Emergent – those that emerge as a better understanding of the system develops.
Consequential – those that result from the introduction of the system.
Compatibility – those that change due to changing systems or processes within the organization.

48. Requirements management planning requires decisions on:
Requirements identification – how requirements will be individually identified
A change management process – to be followed when analyzing the impact and costs of 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

49. Traceability…
…is concerned with the relationships between requirements, their sources, and the system design.
Types of traceability:
Source traceability – links from requirements to stakeholders who proposed the requirements. (or other sources)
Requirements traceability – links between dependent requirements.
Design traceability – links from the requirements to the design.

50. CASE tool support
Requirements storage – in a secure, managed data store
Change management – a workflow process whose stages can be defined and information flow between the stages partially automated
Traceability management – automated discovery and documentation of relationships between requirements (keyword search, common scenarios, etc.)

51. Change management process
Applied to all proposed requirements changes
Principal stages:
Problem analysis – analyze identified requirements problem and propose specific change(s)
Change analysis and costing – assess effects of change on other requirements
Change implementation – modify requirements document (+ system design and implementation, as necessary) to reflect the change

52. Change management process (cont’d)

53. Key points
The RE process includes a feasibility study, elicitation and analysis, specification, and validation.
Elicitation and analysis involves requirements discovery, classification and organization, prioritization and negotiation, and documentation.
(cont'd)

54. Key points (cont’d)
Systems have multiple stakeholders with different viewpoints and requirements.
Social and organization factors influence system requirements.
Requirements validation is concerned with checks for validity, consistency, complete-ness, realism, and verifiability.
(cont'd)

55. Key points (cont’d)
Business, organizational, and technical changes inevitably lead to changing requirements.
Requirements management involves careful planning and a change manage-ment process.

56. Requirements Engineering Process
Chapter 7
Requirements Engineering Process