The concept of goal may be used to model intentions of human actors, such as requirements analysts or designers, as well as the reasons for pro-active behaviour of software agents. This short paper describes three ongoing research e orts on the application of the Goal-Oriented paradigm to system requirements analysis, system design and development of self-adaptive software agents.
The concept of goal, as a state of a airs that an actor (human, organization
or system) wants to achieve, together with social aspects and other intentional
concepts de ne the Goal-Oriented (GO) paradigm that has been largely studied
and applied in Requirements Engineering (RE) since more than ten years [
Evidences of the usefulness of the GO paradigm can be found in a variety of real world experiences that exploited available GO methodologies that support software system development activities ranging from requirements acquisition, analysis and understanding, to design and test cases derivation.
A key feature of the GO paradigm is that of allowing to model and reason about alternatives. These alternatives are usually represented in terms of OR-decompositions of goals or tasks, which lead to the de nition of goal trees, whose alternative paths may be evaluated against possible situations of bene t, drawback or con ict.
This paper summarizes three ongoing research e orts at FBK-IRST in which the GO paradigm plays a central role at support of decision making for domain and system analysts, system designers and also for proactive arti cial agents, in di erent contexts: (i) when analysts have to decide about the compliance of a set of the system's requirements with respect to law; (ii) when designers have to choose a suitable design pattern; (iii) when software agents of a self-adaptive system have to decide at run-time which one among their alternative sub-goals to achieve, while attempting to satisfy the main goals assigned to them by the designers. 2
Laws and regulations address processes and associated information systems within organizations. Available methods and techniques for system design give little support to the requirements engineer when analysing the impact of those regulations during the de nition of requirements for a new system, or when an existing organization has to restructure and re-engineer its operation in order to achieve compliance.
Goal-oriented requirements engineering rests on the idea of deriving the requirements for a software system from the analysis of the goals that the systemto-be will support once developed and deployed. However, when the stakeholders are addressed by laws, the system-to-be has to be aligned with the legal prescriptions, too, and goals per se do not provide information about such an alignment. This is the problem of law compliance of goals models. Finding a solution to this problem means nding the assignment of actors' responsibilities (goals) such that if every actor ful ls its goals, then law is respected. To address this problem we adopt a modelling approach which consists in starting from a model of legal prescriptions, and building the model of goals in an incremental way that maintains the alignment with the prescriptions.
The i * modelling language focuses on intentional elements as the key to
describe and understand a given organizational setting. Laws play a di erent
role as they have (i) physical existence as natural language sentences in legal
texts; and (ii) prescription objectives with regard to the organization. The
contribution of the Nomos framework consists in a conceptual binding between the
two conceptions of intentions and regulations. The binding relies on the analysis
of legal sentences, which ultimately allows to identify the juridical concept of
normative proposition (NP), as the most atomic proposition able to carry a
normative semantics, containing information concerning: (i) the subject(s)
addressed by the NP itself; (ii) the legal modality; and (iii) the description of the
object of such modality. The legal modality is one of the eight elementary rights,
classi ed by Hohfeld [
In order to support modelling of laws and compliance solutions, the i *
metamodel (in the variant proposed by the Tropos methodology [
As future work, we are investigating the use of argumentation framework in order to support the acceptability of compliance solutions. 3
Software patterns are reusable solutions to recurring design problems and |
since their de nition | are considered a mainstream of software reuse practice.
They are typically documented with a textual description of the context where
they can apply, the purpose for their reuse and forces to balance. For encouraging
the understanding of design patterns and to ease their application during the
design phase, many approaches have been proposed to provide the solution by
using formal, semi-formal graphical notations or logic languages [
We propose to use i * to represent not only the pattern solution, but also
the whole reasoning process that led to its formation, including motivation,
trade-o s and alternatives [
The proposed abstraction considers the design activity as the application area in which we apply the i * framework, and the Designer as the main Actor of the design activity, whose job is to balance design forces coming from the system to be modelled. The designer's activities arise from needs, such as: (i) the achievement of Design Goals to solve speci c design problem emerging during the modelling of the system, and (ii) the compliance with Design Properties (or soft goals) that specify qualities of the system. In this context a pattern is a collection of collaborating roles, intended as autonomous holder of design intentions that are delegated of some responsibilities from the designer, namely: (i) design goals/soft- goals to be achieved, (ii) design tasks for introducing a well-known solution, and (iii) system elements to introduce or to organize in the solution.
In this approach, the designer is supported with techniques for balancing pattern contextual forces and for customizing the pattern implementation to the speci c application context. We exploit the Strategic Dependency model for representing the high-level responsibility organization of a design pattern, and the Strategic Rationale model for entering in detail in the solution structure.
The Strategic Dependency main role is always the designer who delegates design intentionality to pattern roles. This view allows for highlighting main intents and motivations of a pattern, and it is an instrument for quick selection of the pattern to reuse from a catalogue. On the other side the Strategic Rationale model allows for reasoning on design issues, considering consequences and balancing design alternatives, thus customizing the solution to meet forces coming from the context.
This approach opens new research directions we are working on: (i) to represent | and reason on | pattern composition and con icts, and (ii) the use of an ontology for standardizing design intentional elements, that may help in automatic discovery of patterns to reuse. 4
Self-adaptive Software (SAS) aims at dealing autonomously with unpredictable
changes which occur in the dynamic environment it executes (at run-time), on
the basis of its knowledge and of the objectives it has been designed for. We
aim at de ning a process and a tool-supported design framework to develop
SAS with the necessary knowledge that enables adaptation of their behaviour
at run-time. Belief-Desire-Intention (BDI) agents [
The proposed framework and development process, called Tropos4AS
(Tropos for Adaptive Systems) [
The environment model captures the non-intentional entities involved in,
used and perceived by the SAS, which are necessary for interfacing the system
with the surrounding world. For instance, the environment for a cleaner robot
includes the oor, the dustbins and a battery charging station. These entities
are represented through artifacts [
In extended goal modelling, the goal model is linked with the environment.
The process of goal achievement is related to the environment by de ning the
context where the goal is applicable, the conditions which lead to its adoption,
its achievement and failure states. Di erent goal types further characterise the
process of goal achievement, distinguishing among goals that the SAS has to
achieve in a given situation (e.g. clean a wet oor), goals that the SAS has to
achieve and maintain all along its life cycle (e.g. maintain a battery loaded), and
goals that can be rather described as executing a given procedure (e.g. searching
for dirt). Goal types were already present in the Formal Tropos [
In failure modelling, Tropos4AS aids the designer in anticipating possible failures, giving a process to elicit errors possibly causing them and analysing the possibilities to x them. Entities added to the Tropos4AS meta-model for supporting failure modelling are: failures, representing undesirable states known to the designer for the impossibility to achieve a goal, perceivable errors that may be the cause of these failures, and recovery activities, i.e. actions that the SAS may undertake to recover from errors, preventing failure.
The implementation is based on a tool-supported mapping of goal models to Jadex BDI agent code, maintaining the goal model with its semantics also at runtime. This goal model drive the agent's behaviour at a knowledge level, de ning the relationship between requirements (goals) and the agents' capabilities, and to ensure traceability of run-time choices back to the design.
The main issue in our research agenda concerns the consolidation of the tools supporting the development and testing of self-adaptive software. Moreover, a validation of the framework on more realistic scenarios will be performed, focusing on the adaptive qualities of the system under development.