Components as coalgebras

In the tradition of mathematical modelling in physics and chemistry, constructive formal specification methods are based on the notion of a software model, understood as a state-based abstract machine which persists and evolves in time, according to a behavioural model capturing, for example, partiality or (different degrees of) nondeterminism. This can be identified with the more prosaic notion of a software component advocated by the software industry as ‘building block’ of large, often distributed, systems. Such a component typically encapsulates a number of services through a public interface which provides a limited access to a private state space, paying tribute to the nowadays widespread object-oriented programming principles. The tradition of communicating systems formal design, by contrast, has developed the notion of a process as an abstraction of the behavioural patterns of a computing system, deliberately ignoring the data and state aspects of software systems. Both processes and components are among the broad group of computing phenomena which are hardly definable (or simply not definable) algebraically, i.e., in terms of a complete set of constructors. Their semantics is essentially observational, in the sense that all that can be traced of their evolution is their interaction with the environment. Therefore, coalgebras, whose theory has recently witnessed remarkable developments, appear as a suitable modelling tool. The basic observation of category theory that universal constructions always come in pairs, has motivated research on the duality between algebras and coalgebras, which provides a bridge between models of static (constructive, data-oriented) and dynamical (observational, behaviour-oriented) systems. At the programming level, the intuitive symmetry between data and behaviour provides evidence of such a duality, in its canonical initial-final specialisation. This line of thought entails both definitional and proof principles, i.e., a basis for the development of program calculi directly based on (actually driven by) type specifications. Moreover, such properties can be expressed in terms of generic programming combinators which are used, not only to calculate programs, but also to program with. Framed in this context, this thesis addresses the following main themes: The investigation of a semantic model for (state-based) software components. These are regarded as concrete coalgebras for some Set endofunctors, with specified initial conditions, and organise themselves in a bicategorical setting. The model is able to capture both behavioural issues, which are usually left implicit in state-based specification methods, and interaction through structured data, which is usually a minor concern on process calculi. Two basic cases are considered entailing, respectively, a ‘functional’ and an ‘object-oriented’ shape for components. Both cases are parametrized by a model of behaviour, introduced as a strong (usually commutative) monad. The development of corresponding component calculi, also parametric on the behaviour model, which adds to the genericity of the approach. The study of processes and the ‘reconstruction’ of classical (CCS-like) process calculi on top of their representation as inhabitants of (the carriers of) final coalgebras, in an essentially pointfree, calculational style. An overall concern for genericity, in the sense that models and calculi for both components and processes are parametric on the behaviour model and the interaction discipline, respectively. The animation of both processes and components in CHARITY, a functional programming language entirely based on inductive and coinductive categorical data types. In particular this leads to the development of a process calculi interpreter parametric on the interaction discipline.PRAXIS XXI - Projecto LOGCAMP; POO11/IC-PME/II/S -Projecto KARMA; Fundação para a Ciência e Tecnologia; ALGORITMI Research Center

Second Generation General System Theory: Perspectives in Philosophy and Approaches in Complex Systems

Following the classical work of Norbert Wiener, Ross Ashby, Ludwig von Bertalanffy and many others, the concept of System has been elaborated in different disciplinary fields, allowing interdisciplinary approaches in areas such as Physics, Biology, Chemistry, Cognitive Science, Economics, Engineering, Social Sciences, Mathematics, Medicine, Artificial Intelligence, and Philosophy. The new challenge of Complexity and Emergence has made the concept of System even more relevant to the study of problems with high contextuality. This Special Issue focuses on the nature of new problems arising from the study and modelling of complexity, their eventual common aspects, properties and approaches—already partially considered by different disciplines—as well as focusing on new, possibly unitary, theoretical frameworks. This Special Issue aims to introduce fresh impetus into systems research when the possible detection and correction of mistakes require the development of new knowledge. This book contains contributions presenting new approaches and results, problems and proposals. The context is an interdisciplinary framework dealing, in order, with electronic engineering problems; the problem of the observer; transdisciplinarity; problems of organised complexity; theoretical incompleteness; design of digital systems in a user-centred way; reaction networks as a framework for systems modelling; emergence of a stable system in reaction networks; emergence at the fundamental systems level; behavioural realization of memoryless functions

Musical eutopias: A positive critique of popular musics & mediated listening, with particular reference to the BBC & public service radio.

Musical eutopias offers positive critiques of the socio-cultural aspects of popular musics, the medium of radio in general, and the British Broadcasting Corporation in particular. Marxian critiques of what Ms9, together with normative, socialist visions of what 'ought' to be, are reviewed with reference to radio's listening subjects and broadcasting ideals. Arguably, popular musics embraced by radio only offer a dystopian standardisation for a mass audience. However, it is mooted here that socio- cultural knowledges mediated by a public service broadcaster can contribute positively to a subject's negotiation of modernity and the objective world. The humanistic potentials of music and broadcasting are considered using two conceits: (1) Sir Thomas Mote's diagnostic benchmark of desired alternatives and perfection: Utopia and (2) Utopia's 'desublimation' in More's quasi-antonymic term, eutopia which is an actual site of resources and relative goodness. To sift for music's Utopia and the eutopian aspects of Theodor Adorno's 'music in radio', the writings of Ernst Bloch, Herbert Marcuse and Jurgen Habermas are reassessed and joined by new Utopian theory from Caryl Flinn, Stephen Eric Bronner and allied thinkers. The cultural and allegorical dimensions of music, and the institutional histories and ideals of the BBC are examined through the work of Antonio Gramsci, Raymond Williams, Michel Foucault, David Levin, Christopher Norris, Simon Frith, Georgina Born and others. A near-Kantian sensibility, imagination and understanding are argued to develop (after Marcuse) in the musical eutopias of public broadcasting. There, a dialectic of Utopian musical desires, socio-political philosophies and independent professional agency promotes rich aesthetic content and an equitable discursive framework for all. The study concludes mat such in-common, public service eutopias of musical and moral dimensions are still of value for subjects becoming rational, empathetic species beings. Such eutopias might even counter new media solipsism and any instrumentally driven calls for broadcast reform. Thesis word total: 79,929. Excludes indented quotations, footnotes, appendices, references and bibliography

Deadlock-Free Absorption of Barrier Synchronisations

This paper validates and generalises an optimisation arising in the compilation of while loops in data-parallel languages for MIMD shared memory architectures. Dependencies in the source program force the introduction of global synchronisations in the target MIMD program; yet, an efficient compilation must decrease the number of these costly operations. In this context, Hatcher and Quinn have proposed an optimisation that consists in splitting the original loop in two consecutive loops: a computation loop without additional control dependencies and a waiting loop to ensure global termination. We prove its correctness in the axiomatic semantics of Owicki and Gries. We observe that the loops are independent and conclude that this property is more generally applicable than suggested by Hatcher and Quinn's method. Keywords Compilers, Parallel Processing, Program Correctness. Introduction In their description of the data-parallel C language (DPC [5]), Hatcher and Quinn propose an origi..