A systematic study of models of abstract data types

AbstractThe term-generated models of an abstract data type can be represented by congruence relations on the term algebra. Total and partial heterogeneous algebras are considered as models of hierarchical abstract data types.Particular classes of models are studied and it is investigated under which conditions they form a complete lattice. This theory allows also to describe programming languages (and their semantic models) by abstract types. As example we present a simple deterministic stream processing language

A timeband framework for modelling real-time systems

Complex real-time systems must integrate physical processes with digital control, human operation and organisational structures. New scientific foundations are required for specifying, designing and implementing these systems. One key challenge is to cope with the wide range of time scales and dynamics inherent in such systems. To exploit the unique properties of time, with the aim of producing more dependable computer-based systems, it is desirable to explicitly identify distinct time bands in which the system is situated. Such a framework enables the temporal properties and associated dynamic behaviour of existing systems to be described and the requirements for new or modified systems to be specified. A system model based on a finite set of distinct time bands is motivated and developed in this paper

Specification of Dynamic Reconfiguration in the Context of Input/Output Relations

Abstract: Recent advances in telecommunication and software technology have mo-tivated the study of components with dynamically changing syntactic interfaces. Formal development methods are traditionally directed towards components with static inter-faces. We investigate this short-coming of formal development methods and outline how it can be overcome. We start by presenting a semantic model for interactive components communicating asynchronously by message passing. On the top of this model we build a simple specifi-cation language directed towards components with static interfaces. Then we generalise this language to handle components with dynamic interfaces. We introduce operators fo

Service Renaming in Component Composition

In component-based systems, the behavior of components is usually described at component interfaces and the components are characterized as requester (active) and provider (reactive) components. Two interacting components are considered compatible if all possible sequences of services requested by one component can be provided by the other component. This concept of component compatibility can be extended to sets of interacting components, however, in the case of several requester components interacting with one or more provider components, as is typically the case of cleint-server applications, the requests from different components can be interleaved and then verifying component compatibility must take into account all possible interleavings of requests. Such interleaving of requests can lead to unexpected behavior of the composed system, e.g. a deadlock can occur. Service renaming is proposed as a method of systematic eliminating of such unexpected effects and streamlining component compositions

RiskStructures : A Design Algebra for Risk-Aware Machines

Machines, such as mobile robots and delivery drones, incorporate controllers responsible for a task while handling risk (e.g. anticipating and mitigating hazards; and preventing and alleviating accidents). We refer to machines with this capability as risk-aware machines. Risk awareness includes robustness and resilience, and complicates monitoring (i.e., introspection, sensing, prediction), decision making, and control. From an engineering perspective, risk awareness adds a range of dependability requirements to system assurance. Such assurance mandates a correct-by-construction approach to controller design, based on mathematical theory. We introduce RiskStructures, an algebraic framework for risk modelling intended to support the design of safety controllers for risk-aware machines. Using the concept of a risk factor as a modelling primitive, this framework provides facilities to construct, examine, and assure these controllers. We prove desirable algebraic properties of these facilities, and demonstrate their applicability by using them to specify key aspects of safety controllers for risk-aware automated driving and collaborative robots