7,430 research outputs found
Feature Interaction Analysis Using Z
No full textFeature Interaction is a well-known problem in telecommunications service provision. Feature interactions arise at different phases in the service creation process. Interactions may appear in the specifications that describe services from the users viewpoint. Equally, specifications that appear to have no interactions from the user viewpoint may interact at the implementation level because they are designed in such a way that they share some network resources. We have examined the use of the formal notation Z in analysing interactions in user-viewpoint service specifications
A CSP Approach to Action Systems
No full textThe communicating sequential processes (CSP) formalism, introduced by Hoare, is an event-based approach to distributed computing. The action-system formalism, introduced by Back & Kurki-Suonio, is a state-based approach to distributed computing. Using weakest-precondition formulae, Morgan has defined a correspondence between action systems and the failures-divergences model for CSP. Simulation is a proof technique for showing refinement of action systems. Using the correspondence of Morgan, Woodcock & Morgan have shown that simulation is sound and complete in the CSP failures-divergences model. In this thesis, Morgan's correspondence is extended to the CSP infinite- traces model in order to deal more properly with unbounded nondeterminism. It is shown that simulation is sound in the infinite-traces model, though completeness is lost in certain cases. The new correspondence is then extended to include a notion of internal action. This allows the definition of a hiding operator for action systems that is shown to correspond to the CSP hiding operator. Rules for simulation steps involving internal actions are developed. A parallel operator for action systems is defined, in which interaction is based on synchronisation over shared actions. This operator is shown to correspond to the CSP parallel operator. The correspondence between action systems and CSP is extended again so that actions may have input and output parameters. This allows parallel action- systems to pass values on synchronisation. The original motivation for the work described in this thesis was the use of the action system formalism in the development of telecommunications systems, where interaction is often based on synchronised value-passing. The techniques developed here are applied to a series of case studies involving telecommunications-type systems. The techniques are used to refine and decompose abstract specifications of these systems into parallel sub-systems that interact via synchronised value-passing
Refinement and decomposition of value-passing action systems in the refinement calculus
No full textThe action system formalism [3] is a state-based approach to distributed computing. In this paper, it is shown how the action system formalism may be used to describe systems that interact with their environment through synchronised value-passing. Definitions and rules are presented for refining and decomposing such action systems into distributed implementations in which internal communication is also based on synchronised value-passing. Specification and refinement is similar to the refinement calculus approach [1, 10, 12]. The theoretical basis for communication and distribution is Hoare's CSP [6]. Use of the refinement and decomposition rules is illustrated by the design of an unordered buffer
Action Systems, Unbounded Nondeterminism, and Infinite Traces
No full textMorgan has described a correspondence between Back's action systems and the conventional failures-divergences model of Hoare's communicating sequential processes (CSP) formalism. However, the CSP failures-divergences model does not treat unbounded nondeterminism, although unbounded nondeterminism arises quite naturally in action systems; to that extent, the correspondence between the two approaches is inadequate. Fortunately there is an extended infinite traces model of CSP developed by Roscoe which treats unbounded nondeterminism. We extend the CSP-action system correspondence, using that model instead, to take the unbounded nondeterminism of action systems properly into account. In passing, we develop a definition of the weakest precondition under which an infinite heterogeneous trace of actions is enabled
Supporting reuse mechanisms for developments in event-b: composition
No full textThe development of specifications often is a combination of smaller sub-components. Focusing on reuse, an interesting perspective is to formally define the combination of sub-components through refinement steps, reusing their properties and generating larger systems. The previous situation suggests the application of a reuse mechanism: composition. Event-B is a formal method that allows modelling and refinement of systems. The combination and reuse of existing sub-components is not currently supported in Event-B. We propose the development of composition by extending the Event-B formalism as an option for developing larger models, focusing in distributed systems. A tool is developed to support the shared event composition in the Rodin platform. Properties and proof obligations of sub-components are reused and sufficient proof obligations are generated to ensure valid composed models
Exploring Summation and Product Operators in the Refinement Calculus
No full textProduct and summation operators for predicate transformers were introduced by Naumann and by Martin using category theoretic considerations. In this paper, we formalise these operators in the higher order logic approach to the refinement calculus of Back and von Wright, and examine various algebraic properties of these operators. There are several motivating factors for this analysis. The product operator provides a model of simultaneous execution of statements, while the summation operator provides a simple model of late binding. We also generalise the product operator slightly to form an operator that corresponds to conjunction of specifications. We examine several applications of the these operators showing, for example, how a combination of the product and summation operators could be used to model inheritance in an object-oriented programming language
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