Are there new models of computation? Reply to Wegner and Eberbach

Wegner and Eberbach[Weg04b] have argued that there are fundamental limitations to Turing Machines as a foundation of computability and that these can be overcome by so-called superTuring models such as interaction machines, the [pi]calculus and the $-calculus. In this paper we contest Weger and Eberbach claims

Communication requirements for team automata

Compatibility of components is an important issue in the quest for systems of systems that guarantee successful communications, free from message loss and indefinite waiting for inputs. In this paper, we investigate compatibility in the context of systems consisting of reactive components which may communicate through the synchronised execution of common actions. We model such systems in the team automata framework, which does not impose any a priori restrictions on the synchronisation policy followed to combine the components. We identify a family of representative synchronisation types based on the number of sending and receiving components participating in synchronisations. Then, we provide a generic procedure to derive, for each synchronisation type, requirements for receptiveness and for responsiveness of team automata that prevent that outputs are not accepted and inputs are not provided, respectively. Due to the genericity of our approach w.r.t. synchronisation policies, we can capture compatibility notions for various multi-component system models known from the literature.Peer ReviewedPostprint (author's final draft

Do technologies have politics? The new paradigm and pedagogy in networked learning

This paper explores the relationships between the technologies deployed in networked and e-Learning and the pedagogies and politics associated with them. Networked learning and the related move to e-Learning are coincident with the globalisation, commodification and massification of Higher Education. It examines the hard and soft forms of technological determinism (TD) found in the current advocacy of technological futures for Higher Education. Hard TD claims that new technologies bring about changes in the pedagogy found in networked learning and that these changes have a socially equalising or democratic effect. Soft TD claims that these changes are not the inevitable outcomes of technology but goes on to suggest that successful use of the technology rests upon exactly the same changes. These changes have been characterised as a ‘new paradigm’ in education

Coherence Generalises Duality: A Logical Explanation of Multiparty Session Types

Wadler introduced Classical Processes (CP), a calculus based on a propositions-as-types correspondence between propositions of classical linear logic and session types. Carbone et al. introduced Multiparty Classical Processes, a calculus that generalises CP to multiparty session types, by replacing the duality of classical linear logic (relating two types) with a more general notion of coherence (relating an arbitrary number of types). This paper introduces variants of CP and MCP, plus a new intermediate calculus of Globally-governed Classical Processes (GCP). We show a tight relation between these three calculi, giving semantics-preserving translations from GCP to CP and from MCP to GCP. The translation from GCP to CP interprets a coherence proof as an arbiter process that mediates communications in a session, while MCP adds annotations that permit processes to communicate directly without centralised control

Experimental Aspects of Synthesis

We discuss the problem of experimentally evaluating linear-time temporal logic (LTL) synthesis tools for reactive systems. We first survey previous such work for the currently publicly available synthesis tools, and then draw conclusions by deriving useful schemes for future such evaluations. In particular, we explain why previous tools have incompatible scopes and semantics and provide a framework that reduces the impact of this problem for future experimental comparisons of such tools. Furthermore, we discuss which difficulties the complex workflows that begin to appear in modern synthesis tools induce on experimental evaluations and give answers to the question how convincing such evaluations can still be performed in such a setting.Comment: In Proceedings iWIGP 2011, arXiv:1102.374

Experimental survey of FPGA-based monolithic switches and a novel queue balancer

This paper studies small to medium-sized monolithic switches for FPGA implementation and presents a novel switch design that achieves high algorithmic performance and FPGA implementation efficiency. Crossbar switches based on virtual output queues (VOQs) and variations have been rather popular for implementing switches on FPGAs, with applications in network switches, memory interconnects, network-on-chip (NoC) routers etc. The implementation efficiency of crossbar-based switches is well-documented on ASICs, though we show that their disadvantages can outweigh their advantages on FPGAs. One of the most important challenges in such input-queued switches is the requirement for iterative scheduling algorithms. In contrast to ASICs, this is more harmful on FPGAs, as the reduced operating frequency and narrower packets cannot “hide” multiple iterations of scheduling that are required to achieve a modest scheduling performance.Our proposed design uses an output-queued switch internally for simplifying scheduling, and a queue balancing technique to avoid queue fragmentation and reduce the need for memory-sharing VOQs. Its implementation approaches the scheduling performance of a state-of-the-art FPGA-based switch, while requiring considerably fewer resources