7 research outputs found
Event Systems and Access Control
We consider the interpretations of notions of access control (permissions,
interdictions, obligations, and user rights) as run-time properties of
information systems specified as event systems with fairness. We give proof
rules for verifying that an access control policy is enforced in a system, and
consider preservation of access control by refinement of event systems. In
particular, refinement of user rights is non-trivial; we propose to combine
low-level user rights and system obligations to implement high-level user
rights
Refinement Calculus of Reactive Systems
Refinement calculus is a powerful and expressive tool for reasoning about
sequential programs in a compositional manner. In this paper we present an
extension of refinement calculus for reactive systems. Refinement calculus is
based on monotonic predicate transformers, which transform sets of post-states
into sets of pre-states. To model reactive systems, we introduce monotonic
property transformers, which transform sets of output traces into sets of input
traces. We show how to model in this semantics refinement, sequential
composition, demonic choice, and other semantic operations on reactive systems.
We use primarily higher order logic to express our results, but we also show
how property transformers can be defined using other formalisms more amenable
to automation, such as linear temporal logic (suitable for specifications) and
symbolic transition systems (suitable for implementations). Finally, we show
how this framework generalizes previous work on relational interfaces so as to
be able to express systems with infinite behaviors and liveness properties
Generating non-conspiratorial executions
Avoiding conspiratorial executions is useful for debugging, model checking or refinement, and helps implement several wellknown
problems in faulty environments; furthermore, avoiding non-equivalence robust executions prevents conflicting
observations in a distributed setting from occurring. Our results prove that scheduling pairs of states and transitions in a strongly
fair manner suf-fices to prevent conspiratorial executions; we then establish a formal connection between conspiracies and
equivalence robustness; finally, we present a transformation scheme to implement our results and show how to build them into a
well-known distributed scheduler. Previous results were applicable to a subset of systems only, just attempted to characterise
potential conspiracies, or were tightly bound up with a particular interaction model.Comisión Interministerial de Ciencia y Tecnología TIC2003-02737-C0
Event Systems and Access Control
We consider the interpretations of notions of access control (permissions, interdictions, obligations, and user rights) as run-time properties of information systems specified as event systems with fairness. We give proof rules for verifying that an access control policy is enforced in a system, and consider preservation of access control by refinement of event systems. In particular, refinement of user rights is non-trivial; we propose to combine low-level user rights and system obligations to implement high-level user rights
Refinement of Fair Action Systems
An action system is a framework for describing parallel or distributed systems, for which the refinement calculus offers a formalisation of the stepwise development method. Fairness is an important notion in modelling parallel or distributed systems, and this paper investigates a calculus for refinement of fair action systems. Simulations, which are proof techniques for refinement, are extended to verify fair action systems. Our work differs from others' in that the additional condition concerning fairness is expressed through termination of related iteration statements. For this purpose, existing proof rules for termination are extended. In the tradition of the refinement calculus, our approach to fairness is based on techniques developed mainly for sequential programming. 1. Introduction An action system is a framework for describing parallel or distributed systems. It focuses on specifying the logical behaviours of the systems by a collection of actions . Actions are expressed in ..