1 Enhancing Requirements Engineering by Quality Modelling: a structured Framework Paolo Donzelli Dept of Informatics Office of the Prime Minister Rome, Italy (Cranfield University, RMCS – Shrivenham UK) novembre 2001

2 Outline Problem description The Requirements Engineering Framework The Framework at work: a case study From RE to system implementation

3 Problem description

4 Introducing an IT system into an organisation a successful system implementation relies on a firm understanding of the application domain our ability of envisioning its impact but the application domain is far from being stable drives the IT system development but must evolve to exploit the system capabilities The system must become an "organic" component of the re-engineered company (the to- be company)

5 Envisioning the to-be company (a difficult task) The system and its application domain form a larger social-technical system whose overall needs are the ones to be fulfilled. Organisations are made of people: the goals, the expectations, and the needs of all the stakeholders, have to be explicitly addressed Customer satisfaction becomes an organisation-wide concept, beyond the simple individual customer or user point of view.

6 Advances in Requirements Engineering (1) Process modelling-based techniques have been suggested to support the Early RE Phases (requirements discovery, validation and verification), by providing a collaborative environment between analysts and stakeholders to: understand the application domain translate application domain needs into system requirements design the to-be company (by reasoning through feasible alternatives) (i*)

7 the WHY as driving factor of the requirements discovery/modelling process (KAOS – I*) Advances in Requirements Engineering (2)

8 Genesis of the proposed RE Framework (1) adopt new RE techniques (i.e. process modelling-based and “why”-oriented approaches) encompass Quality Modelling approaches, to better deal with stakeholders’ quality issues move from “slow, reactive, adversarial, separated software engineering and systems engineering processes to unified, concurrent processes”, which will also include business process reengineering.

9 Genesis of the proposed RE Framework (2) Reasoning about the Why, the What and the How

10 Main Objectives Support discovery, and early verification and validation of both user-oriented and organisation-oriented requirements Facilitate envisioning and designing the to-be company Force reasoning about non-functional requirements since the outset of the project, while dealing with functional ones Soft goals play a central role, providing a systematic and organized way of handling non-functional requirements  constraints in operational terms, or fit criteria for assessment purposes!

11 The Requirements Engineering Framework Main characteristics, Notation, Process

12 The RE Framework: main characteristics Process Soft Goal modelling Hard Goal modelling Organisation modelling case study

13 Organisation Modelling (1) deals with the application domain structure basic elements

14 Organisation Modelling (2) complex agent simple agent

15 Soft Goal Modelling produces operational definitions of the soft goals, decomposing them into sub hard goals and constraints

16 Hard Goal Modelling determines how to achieve hard goals, by decomposing them into sub hard goals and tasks

17 Combining soft and hard goal models Agent’s behaviour (simple or complex)

18 Applying the Framework: the process Development Flow from top organisational level, down to simple agents level, the models feed each others, in a continuous loop. The complete organisation model will result into a flat network of interrelated goals, tasks, and resources, with agents acting as a modularization mechanism Elicitation and Validation Flow where interaction with the stakeholders occurs Verification Flow to guarantee consistency between models

19 A Case Study

20 The case study Strongly interrelated with the application domain, highly complex and expensive, they require a RE process strongly focused on the early verification and validation Synthetic Environments are distributed interactive simulations of real-world systems, used to support operational, political and economic decisions RE process for a ground-based simulator suitable to investigate the feasibility of equipping an aircraft with a new avionics sub-system

21 A ground-based simulator

22 The Organisation Model from goals to req.s clashing req.s

23 Soft goal upon the Project Leader

24 Hard goals upon the Project Leader

25 From high level goals to system requirements there is not one single set of global goals that has to be achieved (from which the others are refined in a top-down way) an organisation consists of numerous processes occurring simultaneously, involving various agents, following different paths, and intersecting each other an agent may operate as goal generator, as well as a goal transformer goals propagate through the organisation in complex patterns and may even conflict It is from the set of goals and constraints placed upon the system that the final requirements can be obtained

26 Clashing Requirements: detecting and resolving them through soft goals Agents may have different opinions, and their goals collide. How can Soft Goals help? provide a way to reason about trade-offs, to freeze temporary solutions, and to formalise final decisions encourage interactions and a common terminology force us to clarify, very early in the project, concepts that are usually left blurred until it is too late (or too expensive) for any corrective intervention

27 “Realism” soft goal for the Flight Test Crew

28 “Realism” soft goal for the Avionics System Expert

29 Resolved “Realism” soft goal

30 Deliverables of the RE Framework

31 Have the objectives been achieved? The RE Framework improves the early-stage verification and validation of the requirements of a IT system: Verification is improved by reconciling the different models Validation is improved because of the visibility of the decisions made by stakeholders. Application results suggest that the Framework offers benefits to accreditation and maintenance activities, mainly thanks to the two-way goal requirement link Accreditation should be made easier by tracing the IT system properties to application domain needs Maintainability is improved because changes in the application domain may be easily linked to system changes.

32 From RE to System Implementation

33 Deriving the System Requirements Architecture the RE framework allows us to model the application domain at a social-technical level, by providing a systematic approach to deal with agents, soft goals, hard goals and their incremental refinement requirements are expressed as a collection of hard goals and constraints placed upon the system by other agents

34 An Extract from the Organisation Model

35 The RE Framework outcome a set of Hard Goals and Constraints

36 RE Framework as forerunner for UML the front-end activity of any UML-based approach is the use-case modelling, i.e. capturing the ways in which the users intend to interact with it. use-case analysis can benefit from supporting methods (Business Process Modelling and Black Box approaches) that help to identify both the actors, and their goals the output from our RE Framework, in the form of a set of hard goals and constraints placed upon the system by well-defined agents, is entirely consistent with this.

37 Use-cases as a Goal-refinement Strategy a hard goal can lead to one or more use- cases constraints will become non-functional requirements use-cases offer a systematic and intuitive means of capturing functional requirements constraints enrich and complete the use- cases, by providing a systematic and intuitive means of dealing with non- functional requirements.

38 Avionics System Expert: Use-case Diagram constraints goals

39 The Use-case Diagram

40 Building the conceptual model: the class diagram