1. 1 / 18 CS 425/625 Software Engineering Requirements Engineering Processes Based on Chapter 6 of the textbook [Somm00] Ian Sommerville, Software Engineering, 6 th Ed., Addison-Wesley, 2000 and on the Ch6 PowerPoint presentation available at the book’s web-site: www.comp.lancs.ac.uk/computing/resources/IanS/SE6/Slides/index.html September 22, 2003

2. 2 / 18 Outline n n Introduction n n Feasibility Studies n n Requirements Elicitation and Analysis n n Requirements Validation n n Requirements Management

3. 3 / 18 Introduction n n The requirements engineering process [Fig. 6.1, Somm00]

4. 4 / 18 Feasibility Studies n n The input of a feasibility study is an outline description of the system n n The output is a report which recommends or not continuing the development process n n Activities: u u Information collection u u Information assessment u u Report writing n n Questions asked during feasibility studies: u u What contribution brings the new system to the organization? u u Can the system be built given its specific constraints? u u Can the system be integrated with already existing systems in the organization?

5. 5 / 18 Requirements Elicitation & Analysis…… n n Involves work with costumers and end-users to define the services and constraints of the system n n Stakeholders = people who have direct or indirect influence on the way the system’s requirements are shaped n n Challenges of requirements elicitation and analysis: u u Stakeholders not clear about what they want u u Domain knowledge implicitly assumed u u Various ways of expressing requirements u u Political considerations involved u u Dynamic business and economic environment

6. 6 / 18.Requirements Elicitation & Analysis…. n n The requirements elicitation & analysis process [Fig. 6.2, Somm00]

7. 7 / 18..Requirements Elicitation & Analysis… n n Three techniques for requirements elicitation and analysis: u u Viewpoint-oriented elicitation: various stakeholders’ points of view are taken into consideration (section 6.2.1 in [Somm00]) u u Scenario-based elicitation and analysis: using concrete sections of operations the details of the system’s requirements emerge u u Ethnography: technique that focuses on understanding social and organizational requirements (section 6. 2.3 in [Somm00])

8. 8 / 18 …Requirements Elicitation & Analysis.. n n Event scenarios [Fig. 6.10, SE-6]

9. 9 / 18 ….Requirements Elicitation & Analysis. n n Use-cases [Fig. 6.12, Somm00]

10. 10 / 18 …..Requirements Elicitation & Analysis n n Sequence diagram [Fig. 6.13, Somm00]

11. 11 / 18 Requirements Validation.. n n Requirements validation has the goal of ensuring that the system requirements do represent in fact what the user wants n n It is a form of requirements analysis which works with a complete set of requirements n n Very important activity since discovering problems with requirements at this stage saves a significant amount of money

12. 12 / 18.Requirements Validation. n n Types of checks for requirements validation: u u Validity checks u u Consistency checks u u Completeness checks u u Reality/feasibility checks u u Verifiability n n Techniques for requirements validation: u u Reviews u u Prototyping u u Test-case generation u u Automated consistency analysis

13. 13 / 18..Requirements Validation n n Automated consistency analysis of requirements [Fig. 6.15, Somm00]

14. 14 / 18 Requirements Management…. n n Requirements management is necessary because new requirements tend to emerge continuously. Its goal is to understand and control new requirements n n Reasons for new requirements: u u Large systems have many users, with distinct sets of requirements, preferences, and priorities u u Differences between the views of customers (who pay for the system) and end-users (who actually work with the system) u u The system’s environment evolves continuously

15. 15 / 18.Requirements Management… n n Requirements from an evolution standpoint: u u Enduring requirements u u Volatile requirements:   Mutable   Emergent   Consequential   Compatibility requirements n n Requirements management planning involves decisions on: u u Identification of new requirements u u Change management process u u Traceability of requirements u u Tool support

16. 16 / 18..Requirements Management.. n n Requirements Evolution [Fig. 6.16, Somm00]

17. 17 / 18 …Requirements Management. n n Traceability Matrix [Fig. 6.18, Somm00]

18. 18 / 18 ….Requirements Management n n Change management [Fig. 6.19, SE-6]