Requirements Engineering Processes l Processes used to discover

Requirements Engineering Processes l Processes used to discover, analyse and validate system requirements ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 1

Requirements engineering processes l Generic activities common to all processes • • Requirements elicitation Requirements analysis Requirements validation Requirements management ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 4

The requirements engineering process ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 5

Feasibility studies l 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 ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 6

Feasibility study implementation l 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? ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 7

Elicitation and analysis l l Technical staff work 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 ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 8

Problems of requirements analysis l l l Stakeholders don’t know what they really want Stakeholders may want more than is feasible 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 change ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 9

The requirements analysis process ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 10

Viewpoint-oriented elicitation l l l Stakeholders are members of different groups with different problem viewpoints Valuable approach because it recognizes the potential for requirements conflicts, and explicitly focuses on different perspectives Different methods have different kinds of “viewpoints”, with different strengths and weaknesses ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 13

ATM system viewpoints l l l l Bank customers Representatives of other banks Hardware and software maintenance engineers Marketing department Bank managers and counter staff Database administrators and security staff Communications engineers Personnel department ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 15

External viewpoints – based on services l l Natural to think of end-users as receivers of system services Viewpoints are a natural way to structure requirements elicitation It is relatively easy to decide if a viewpoint is valid Viewpoints and services may be used to structure non-functional requirements ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 17

The VORD method ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 19

Viewpoint identification ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 21

Viewpoint service information ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 22

Viewpoint data/control ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 23

Viewpoint hierarchy ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 24

Viewpoint documentation VORD standard forms ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 25

Customer/cash withdrawal templates ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 26

Scenarios l l l Scenarios are descriptions of how a system is used in practice People can relate to these more readily Particularly useful for adding detail ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 27

Scenario descriptions l l l System state at the beginning of the scenario Normal flow of events in the scenario What can go wrong and how this is handled Other concurrent activities System state on completion of the scenario ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 28

Event scenarios l l Event scenarios describe how a system responds to the occurrence of some particular event VORD includes a diagrammatic convention for event scenarios. ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 29

Event scenario - start transaction ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 30

Exception description l l Unlike most methods, event scenarios include facilities for describing exceptions In this example, exceptions are • • • Timeout. Invalid card. Stolen card. ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 32

Use cases l l l 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 ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 33

Library use-cases ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 35

Catalogue management ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 36

Social and organisational factors l l l Software systems are used in a social and organisational context. This can influence or even dominate the system requirements Social and organisational factors are not a single viewpoint but are influences on all viewpoints Good analysts must be sensitive to these factors but currently no systematic way to tackle their analysis ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 37

Example l Consider a system which allows senior management to access information without going through middle managers • • • Managerial status. Senior managers may feel that they are too important to use a keyboard. This may limit the type of system interface used Managerial responsibilities. Managers may have no uninterrupted time where they can learn to use the system Organisational resistance. Middle managers who will be made redundant may deliberately provide misleading or incomplete information so that the system will fail ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 38

Focused ethnography l l 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 Problem with ethnography is that it studies existing practices which may have some historical basis which is no longer relevant ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 40

Requirements validation l l Demonstrating that the requirements define the system that the customer really wants Requirements error costs are high so validation is very important ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 43

Requirements checking l l l Validity. Consistency. Completeness. Realism. Verifiability. ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 44

Requirements validation techniques l l Requirements reviews Prototyping Test-case generation Automated consistency analysis ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 45

Requirements reviews l l Regular reviews during requirements definition Both client and contractor staff should be involved Reviews may be formal (with completed documents) or informal. Good communications between developers, customers and users can resolve problems at an early stage ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 46

Review checks l l Verifiability. Comprehensibility. Traceability. Adaptability. ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 47

Automated consistency checking ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 48

Requirements management l l Requirements management is the process of managing changing requirements during the requirements engineering process and system development Requirements are inevitably incomplete and inconsistent ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 49

Requirements change l l l Change in priority of requirements from different viewpoints 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 ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 50

Enduring and volatile requirements l l Enduring requirements. Volatile requirements. ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 52

Classification of volatile requirements l Mutable requirements • l Emergent requirements • l Requirements that emerge as understanding of the system develops Consequential requirements • l Requirements that change due to the system’s environment Requirements that result from the introduction of the computer system Compatibility requirements • Requirements that depend on other systems or organisational processes ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 53

Requirements management planning l 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 ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 54

Traceability l l Traceability is concerned with the relationships between requirements, their sources and the system design Source traceability Requirements traceability Design traceability ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 55

A traceability matrix ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 56

CASE tool support l l l Requirements storage Change management Traceability management ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 57

Requirements change management l Should apply to all proposed changes to the requirements ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 58

Requirements change management ©Ian Sommerville 2000 Software Engineering, 6 th edition. Chapter 6 Slide 59