Dalal Alrajeh

Learning operational requirements from goal models

Goal-oriented methods have increasingly been recognised as an effective means for eliciting, elaborating, analysing and specifying software requirements. A key activity in these approaches is the elaboration of a correct and complete set of opertional requirements, in the form of pre- and trigger-conditions, that guarantee the system goals. Few existing approaches provide support for this crucial task and mainly rely on significant effort and expertise of the engineer. In this paper we propose a tool-based framework that combines model checking, inductive learning and scenarios for elaborating operational requirements from goal models. This is an iterative process that requires the engineer to identify positive and negative scenarios from counterexamples to the goals, generated using model checking, and to select operational requirements from suggestions computed by inductive learning.

Generating obstacle conditions for requirements completeness

Missing requirements are known to be among the major causes of software failure. They often result from a natural inclination to conceive over-ideal systems where the software-to-be and its environment always behave as expected. Obstacle analysis is a goal-anchored form of risk analysis whereby exceptional conditions that may obstruct system goals are identified, assessed and resolved to produce complete requirements. Various techniques have been proposed for identifying obstacle conditions systematically. Among these, the formal ones have limited applicability or are costly to automate. This paper describes a tool-supported technique for generating a set of obstacle conditions guaranteed to be complete and consistent with respect to the known domain properties. The approach relies on a novel combination of model checking and learning technologies. Obstacles are iteratively learned from counterexample and witness traces produced by model checking against a goal and converted into positive and negative examples, respectively. A comparative evaluation is provided with respect to published results on the manual derivation of obstacles in a real safety-critical system for which failures have been reported.

Extracting Requirements from Scenarios with ILP

Requirements Engineering involves the elicitationof high-level stakeholder goals and their refinementinto operational system requirements. A key difficulty is that stakeholders typically convey their goals indirectly through intuitive narrative-style scenarios of desirable and undesirable system behaviour, whereas goal refinement methods usually require goals to be expressed declaratively using, for instance, a temporal logic. Currently, the extraction of formal requirements from scenario-based descriptions is a tedious and error-prone process that would benefit from automated tool support. We present an ILP methodology for inferring requirements from a set of scenarios and an initial but incomplete requirements specification. The approach is based on translating the specification and scenarios into an event-based logic programming formalism and using a non-monotonic ILP system to learn a set of missing event preconditions. The contribution of this paper is a novel application of ILP to requirements engineering that also demonstrate the need for non-monotonic learning.

Elaborating Requirements Using Model Checking and Inductive Learning

The process of Requirements Engineering (RE) includes many activities, from goal elicitation to requirements specification. The aim is to develop an operational requirements specification that is guaranteed to satisfy the goals. In this paper, we propose a formal, systematic approach for generating a set of operational requirements that are complete with respect to given goals. We show how the integration of model checking and inductive learning can be effectively used to do this. The model checking formally verifies the satisfaction of the goals and produces counterexamples when incompleteness in the operational requirements is detected. The inductive learning process then computes operational requirements from the counterexamples and user-provided positive examples. These learned operational requirements are guaranteed to eliminate the counterexamples and be consistent with the goals. This process is performed iteratively until no goal violation is detected. The proposed framework is a rigorous, tool-supported requirements elaboration technique which is formally guided by the engineers knowledge of the domain and the envisioned system.

Using Abduction and Induction for Operational Requirements Elaboration

Abstract Requirements Engineering involves the elicitation of high-level stakeholder goals and their refinement into operational system requirements. A key difficulty is that stakeholders typically convey their goals indirectly through intuitive narrative-style scenarios of desirable and undesirable system behaviour, whereas goal refinement methods usually require goals to be expressed declaratively using, for instance, a temporal logic. In actual software engineering practice, the extraction of formal requirements from scenario-based descriptions is a tedious and error-prone process that would benefit from automated tool support. This paper presents an Inductive Logic Programming method for inferring operational requirements from a set of example scenarios and an initial but incomplete requirements specification. The approach is based on translating the specification and the scenarios into an event-based logic programming formalism and using a non-monotonic reasoning system, called eXtended Hybrid Abductive Inductive Learning, to automatically infer a set of event pre-conditions and trigger-conditions that cover all desirable scenarios and reject all undesirable ones. This learning task is a novel application of logic programming to requirements engineering that also demonstrates the utility of non-monotonic learning capturing pre-conditions and trigger-conditions.

Deriving non-Zeno behaviour models from goal models using ILP

One of the difficulties in goal-oriented requirements engineering (GORE) is the construction of behaviour models from declarative goal specifications. This paper addresses this problem using a combination of model checking and machine learning. First, a goal model is transformed into a (potentially Zeno) behaviour model. Then, via an iterative process, Zeno traces are identified by model checking the behaviour model against a time progress property, and inductive logic programming (ILP) is used to learn operational requirements (pre-conditions) that eliminate these traces. The process terminates giving a non-Zeno behaviour model produced from the learned pre-conditions and the given goal model.

Learning from vacuously satisfiable scenario-based specifications

Scenarios and use cases are popular means for supporting requirements elicitation and elaboration. They provide examples of how the system-to-be and its environment can interact. However, such descriptions, when large, are cumbersome to reason about, particularly when they include conditional features such as scenario triggers and use case preconditions. One problem is that they are susceptible to being satisfied vacuously: a system that does not exhibit a scenarios trigger or a use cases precondition, need not provide the behaviour described by the scenario or use case. Vacuously satisfiable scenarios often indicate that the specification is partial and provide an opportunity for further elicitation. They may also indicate conflicting boundary conditions. In this paper we propose a systematic, semi-automated approach for detecting vacuously satisfiable scenarios (using model checking) and computing the scenarios needed to avoid vacuity (using machine learning).

Inferring operational requirements from scenarios and goal models using inductive learning

Goal orientation is an increasingly recognised Requirements Engineering paradigm. However, integration of goal modelling with operational models remains an open area for which the few techniques that exist are cumbersome and impractical. In particular, the derivation of operational models and operational requirements from goals is a manual and tedious task which is, currently, only partially supported by operationalisation patterns. In this position paper we propose a framework for supporting such tasks by combining model checking and machine learning. As a proof of concept we instantiate the framework to show that progress checks and inductive learning can be used to infer preconditions and hence to support derivation of operational models.

Supporting incremental behaviour model elaboration

Behaviour model construction remains a difficult and labour intensive task which hinders the adoption of model-based methods by practitioners. We believe one reason for this is the mismatch between traditional approaches and current software development process best practices which include iterative development, adoption of use-case and scenario-based techniques and viewpoint- or stakeholder-based analysis; practices which require modelling and analysis in the presence of partial information about system behaviour.Our objective is to address the limitations of behaviour modelling and analysis by shifting the focus from traditional behaviour models and verification techniques that require full behaviour information to partial behaviour models and analysis techniques, that drive model elaboration rather than asserting adequacy. We aim to develop sound theory, techniques and tools that facilitate the construction of partial behaviour models through model synthesis, enable partial behaviour model analysis and provide feedback that prompts incremental elaboration of partial models.In this paper we present how the different research threads that we have and currently are developing help pursue this vision as part of the “Partial Behaviour Modelling—Foundations for Iterative Model Based Software Engineering” Starting Grant funded by the ERC. We cover partial behaviour modelling theory and construction, controller synthesis, automated diagnosis and refinement, and behaviour validation.

Automated goal operationalisation based on interpolation and SAT solving

Goal oriented methods have been successfully employed for eliciting and elaborating software requirements. When goals are assigned to an agent, they have to be operationalised: the agent’s operations have to be refined, by equipping them with appropriate enabling and triggering conditions, so that the goals are fulfilled. Goal operationalisation generally demands a significant effort of the engineer. Although there exist approaches that tackle this problem, they are either informal or at most semi automated, requiring the engineer to assist in the process. In this paper, we present an approach for goal operationalisation that automatically computes required preconditions and required triggering conditions for operations, so that the resulting operations establish the goals. The process is iterative, is able to deal with safety goals and particular kinds of liveness goals, and is based on the use of interpolation and SAT solving.