A Verification Concept for SDL Systems and its Application to the Abracadabra Protocol

Starting from a purely functional description of a communication protocol, we present a method how correctness proofs including safety- and progress properties can be developed systematically with an automatic theorem prover. We show how a complex proof can be divided into smaller ones due to proof arguments typically occurring in the area of protocol verification. Experience with this method shows that proofs can be developed with an acceptable amount of work. 1.1. Introduction The objective we pursue with our work is to verify properties of communication protocols. We start with an automata based description of the protocol and a property p given in terms of firstorder logic. Due to Broy [Bro87,91] we model the behaviour of the protocol agents with functions over streams and the system behaviour with its least fixed point c. If we use this formalism, we can reduce the verification problem to a proof of the theorem lf(c) ® p(c). lf is a logical formula formalizing that c is the least ..

Multi-Object Cooperation in Distributed Object Bases

It is an emerging trend to build large information systems in a component-based fashion where the components follow the concept of object. Applications are constructed by organizing pre-built objects such that they cooperate with each other to perform some task. However, considerable programming effort is required to express multi-object constraints in terms of the traditional message-passing mechanism. This observation lead many authors to suggest communication abstractions in object models. One promising approach is to separate multi-object constraints from the objects and collect them into a separate construct. We call this construct an alliance. Unlike other approaches we allow alliances to involve large sets of long-lived objects which may dynamically vary during the --- also potentially long --- life-time of the alliance. Alliances are not only visible at the specification level but are also computational entities which enforce multi-object constraints at run-time. They do so in..

European international broadcasting and Islamist terrorism in Africa: The case of Boko Haram on <i>France 24</i> and <i>Deutsche Welle</i>

This article examines the relationship between European (international) broadcasting and Islamist terrorism in Africa and positions media portrayal of Boko Haram within the larger picture of Europe’s relations with Africa. Two international broadcasters provide the basis for the analysis: France 24 and Deutsche Welle. The article compares and contrasts their discourse on terrorism to advance several arguments: 1) that through their respective portrayal of Boko Haram and Nigeria both France 24 and Deutsche Welle’s reporting is in line with their respective countries’ foreign policies towards Africa, 2) that discourse on both F24 and DW perpetuates the unequal relationship between African countries and Western powers, 3) that portraying terrorism in terms of ‘clash of civilisations’, as in the case of France 24, may unintentionally contribute to the strengthening of the extremist cause. This is due to the transformation of violent extremism into ‘new wars’. The concept, elaborated in the article, differently explains the logic of extremist behaviour and its relationship with media