Goals capture, at different levels of abstraction, the various objectives the system under consideration should achieve.

Requirements engineering (RE) is concerned with the identification of the goals to be achieved by the envisioned system, the operationalization of such goals into services and constraints, and the assignment of responsibilities for the resulting requirements to agents such as humans, devices, and software. The processes involved in RE include domain analysis, elicitation, specification, assessment, negotiation, documentation, and evolution. Getting highquality requirements is difficult and critical. Recent surveys have confirmed the growing recognition of RE as an area of utmost importance in software engineering research and practice. The paper presents a brief history of the main concepts and techniques developed to date to support the RE task, with a special focus on modeling as a common denominator to all RE processes. The initial description of a complex safetycritical system is used to illustrate a number of current research trends in RE-specific areas such as go...

Abstract—Scenarios are increasingly recognized as an effective means for eliciting, validating, and documenting software requirements. This paper concentrates on the use of scenarios for requirements elicitation and explores the process of inferring formal specifications of goals and requirements from scenario descriptions. Scenarios are considered here as typical examples of system usage; they are provided in terms of sequences of interaction steps between the intended software and its environment. Such scenarios are in general partial, procedural, and leave required properties about the intended system implicit. In the end such properties need to be stated in explicit, declarative terms for consistency/completeness analysis to be carried out. A formal method is proposed for supporting the process of inferring specifications of system goals and requirements inductively from interaction scenarios provided by stakeholders. The method is based on a learning algorithm that takes scenarios as examples/counterexamples and generates a set of goal specifications in temporal logic that covers all positive scenarios while excluding all negative ones. The output language in which goals and requirements are specified is the KAOS goal-based specification language. The paper also discusses how the scenario-based inference of goal specifications is integrated in the KAOS methodology for goal-based requirements engineering. In particular, the benefits of inferring declarative specifications of goals from operational scenarios are demonstrated by examples of formal analysis at the goal level, including conflict analysis, obstacle analysis, the inference of higherlevel goals, and the derivation of alternative scenarios that better achieve the underlying goals. Index Terms—Scenario-based requirements elicitation, inductive inference of specifications, goal-oriented requirements engineering, specification refinement and analysis, lightweight formal methods. 1

Goal orientation is an increasingly recognized paradigm for eliciting, structuring, analyzing and documenting system requirements. Goals are statements of intent ranging from high-level, strategic concerns to low-level, technical requirements on the software-to-be and assumptions on its environment. Achieving goals require the cooperation of agents such as software components, input/output devices and human agents. The assignment of responsibilities for goals to agents is a critical decision in the requirements engineering process as alternative agent assignments define alternative system proposals. The paper describes a systematic technique to support the process of refining goals, identifying agents, and exploring alternative responsibility assignments. The underlying principles are to refine goals until they are assignable to single agents, and to assign a goal to an agent only if the agent can realize the goal. There are various reasons why a goal may not be realizable by an agent, e.g., the goal may refer to variables that are not monitorable or controllable by the agent. The notion of goal realizability is first defined on formal grounds; it provides a basis for identifying a complete taxonomy of realizability problems. From this taxonomy we systematically derive a catalog of tactics for refining goals and identifying agents so as to resolve realizability problems. Each tactics corresponds to the application of a formal refinement pattern that relieves the specifier from verifying the correctness of refinements in temporal logic. Our techniques have been used in two case studies of significant size; excerpts are shown to illustrate the main ideas.

The success of large software engineering projects depends critically on the specification, which must represent the requirements of a large number of people with widely differing perspectives. Conventional approaches to software engineering do not address the process of identifying and integrating these perspectives, but instead concentrate on the maintenance of a single consistent description. This results in a specification which represents only one point of view, often the analyst's, excluding suggestions which do not fit with this view. The processes which led to the adoption of this point of view will go unrecorded, making any rationale attached to such a specification incomplete. Other participants will not be able to validate it properly, as it does not relate to their requirements. This thesis integrates ideas drawn from the study of knowledge acquisition, computer-supported co-operative work and negotiation into a model of the specification activity which allows the capture ...

Formal specifications have been a focus of software engineering research for many years and have been applied in a wide variety of settings. Their industrial use is still limited but has been steadily growing. After recalling the essence, role, usage, and pitfalls of formal specification, the paper reviews the main specification paradigms to date and discuss their evaluation criteria. It then provides a brief assessment of the current strengths and weaknesses of today's formal specification technology. This provides a basis for formulating a number of requirements for formal specification to become a core software engineering activity in the future.

Abstract. Requirements and architecture are two essential inter-related products in the software lifecycle. Software architecture has long been recognized to have a profound impact on non-functional requirements about security, fault tolerance, performance, evolvability, and so forth. In spite of this, very few techniques are available to date for systematically building software architectures from functional and non-functional requirements so that such requirements are guaranteed by construction. The paper addresses this challenge and proposes a goal-oriented approach to architectural design based on the KAOS framework for modeling, specifying and analyzing requirements. After reviewing some global architectural decisions that are already involved in the requirements engineering process, we discuss our architecture derivation process. Software specifications are first derived from requirements. An abstract architectural draft is then derived from functional specifications. This draft is refined to meet domain-specific architectural constraints. The resulting architecture is then recursively refined to meet the various non-functional goals modelled and analyzed during the

The thesis proposes a number of techniques for elaborating requirements constructively from high-level goals. The techniques are based on the KAOS goal-oriented method for requirements engineering. This method consists in identifying goals and refining them into subgoals until the latter can be assigned as responsibilities of single agents such as humans, devices and software. Domain properties and assumptions about the software environment are also used during the goal refinement process. The method supports the exploration of alternative goal refinements and alternative responsibility assignments of goals to agents. It also supports the identification and resolution of conflicts between goals, and the identification and resolution of exceptional agent behaviors, called obstacles, that violate goals and assumptions produced during the goal refinement process. The thesis enriches the KAOS framework through three kinds of techniques: (a) techniques for identifying agents, goal refinements, and alternative responsibility assignments, and for deriving agent interfaces from such responsibility assignments; (b) techniques for deriving operational requirements from goal specifications; (c) techniques for generating obstacles to the satisfaction of idealized goals and assumptions, and for generating alternative obstacle resolutions. The result is a coherent body of systematic techniques for requirements elaboration that are both theoretically well-founded (a formal model of agent is defined) and effective in practice (the techniques are validated on two real case studies of significant size: the London ambulance despatching system, and the Bay Area Rapid Transit train system).

Requirements engineering (RE) is concerned with the elicitation of the objectives to be achieved by the system envisioned, the operationalization of such objectives into specifications of services and constraints, the assignment of responsibilities for the resulting requirements to agents such as humans, devices and software, and the evolution of such requirements over time and across system families. Getting highquality requirements is difficult and critical. Recent surveys have confirmed the growing recognition of RE as an area of primary concern in software engineering research and practice.

E-commerce and m-commerce have dramatically boosted the demand for services which enable ubiquitous access. Ubiquity with its anytime/anywhere/anymedia nature requiring contextaware computing and personalisation calls for new engineering techniques supporting these kind of services. In this paper, we propose the notion of customisation as the uniform mechanism to provide the necessary flexibility with respect to both contextaware computing and personalisation. Customisation is realised in terms of a reflective architecture consisting of context, profile and customisation rule management. Keywords: Modelling, Goal-oriented Software Engineering, Customisation, Ubiquitous Web Applications