Scenarios-based testing of systems with distributed ports

Copyright @ 2011 John Wiley & SonsDistributed systems are usually composed of several distributed components that communicate with their environment through specific ports. When testing such a system we separately observe sequences of inputs and outputs at each port rather than a global sequence and potentially cannot reconstruct the global sequence that occurred. Typically, the users of such a system cannot synchronise their actions during use or testing. However, the use of the system might correspond to a sequence of scenarios, where each scenario involves a sequence of interactions with the system that, for example, achieves a particular objective. When this is the case there is the potential for there to be a significant delay between two scenarios and this effectively allows the users of the system to synchronise between scenarios. If we represent the specification of the global system by using a state-based notation, we say that a scenario is any sequence of events that happens between two of these operations. We can encode scenarios in two different ways. The first approach consists of marking some of the states of the specification to denote these synchronisation points. It transpires that there are two ways to interpret such models and these lead to two implementation relations. The second approach consists of adding a set of traces to the specification to represent the traces that correspond to scenarios. We show that these two approaches have similar expressive power by providing an encoding from marked states to sets of traces. In order to assess the appropriateness of our new framework, we show that it represents a conservative extension of previous implementation relations defined in the context of the distributed test architecture: if we onsider that all the states are marked then we simply obtain ioco (the classical relation for single-port systems) while if no state is marked then we obtain dioco (our previous relation for multi-port systems). Finally, we concentrate on the study of controllable test cases, that is, test cases such that each local tester knows exactly when to apply inputs. We give two notions of controllable test cases, define an implementation relation for each of these notions, and relate them. We also show how we can decide whether a test case satisfies these conditions.Research partially supported by the Spanish MEC project TESIS (TIN2009-14312-C02-01), the UK EPSRC project Testing of Probabilistic and Stochastic Systems (EP/G032572/1), and the UCM-BSCH programme to fund research groups (GR58/08 - group number 910606)

Causality in concurrent systems

Concurrent systems identify systems, either software, hardware or even biological systems, that are characterized by sets of independent actions that can be executed in any order or simultaneously. Computer scientists resort to a causal terminology to describe and analyse the relations between the actions in these systems. However, a thorough discussion about the meaning of causality in such a context has not been developed yet. This paper aims to fill the gap. First, the paper analyses the notion of causation in concurrent systems and attempts to build bridges with the existing philosophical literature, highlighting similarities and divergences between them. Second, the paper analyses the use of counterfactual reasoning in ex-post analysis in concurrent systems (i.e. execution trace analysis).Comment: This is an interdisciplinary paper. It addresses a class of causal models developed in computer science from an epistemic perspective, namely in terms of philosophy of causalit

Acoustic Communication for Medical Nanorobots

Communication among microscopic robots (nanorobots) can coordinate their activities for biomedical tasks. The feasibility of in vivo ultrasonic communication is evaluated for micron-size robots broadcasting into various types of tissues. Frequencies between 10MHz and 300MHz give the best tradeoff between efficient acoustic generation and attenuation for communication over distances of about 100 microns. Based on these results, we find power available from ambient oxygen and glucose in the bloodstream can readily support communication rates of about 10,000 bits/second between micron-sized robots. We discuss techniques, such as directional acoustic beams, that can increase this rate. The acoustic pressure fields enabling this communication are unlikely to damage nearby tissue, and short bursts at considerably higher power could be of therapeutic use.Comment: added discussion of communication channel capacity in section

A LISP-Ada connection

The prototype demonstrates the feasibility of using Ada for expert systems and the implementation of an expert-friendly interface which supports knowledge entry. In the Ford LISP-Ada Connection (FLAC) system LISP and Ada are used in ways which complement their respective capabilities. Future investigation will concentrate on the enhancement of the expert knowledge entry/debugging interface and on the issues associated with multitasking and real-time expert systems implementation in Ada

Bibliographic Review on Distributed Kalman Filtering

In recent years, a compelling need has arisen to understand the effects of distributed information structures on estimation and filtering. In this paper, a bibliographical review on distributed Kalman filtering (DKF) is provided.\ud The paper contains a classification of different approaches and methods involved to DKF. The applications of DKF are also discussed and explained separately. A comparison of different approaches is briefly carried out. Focuses on the contemporary research are also addressed with emphasis on the practical applications of the techniques. An exhaustive list of publications, linked directly or indirectly to DKF in the open literature, is compiled to provide an overall picture of different developing aspects of this area