Alexander V. Shafarenko

A GENTLE INTRODUCTION TO S-NET: TYPED STREAM PROCESSING AND DECLARATIVE COORDINATION OF ASYNCHRONOUS COMPONENTS

We present the design of S-NET, a coordination language and component technology based on stream processing. S-NET achieves a near-complete separation between application code, written in a conventional programming language, and coordination code, written in S-NET itself. S-NET boxes integrate existing sequential code as stream-processing components into streaming networks, whose construction is based on algebraic formulae built out of four network combinators. Subtyping on the level of boxes and networks and a tailor-made inheritance mechanism achieve flexible software reuse.

Asynchronous Stream Processing with S-Net

We present the rationale and design of S-Net, a coordination language for asynchronous stream processing. The language achieves a near-complete separation between the application code, written in any conventional programming language, and the coordination/communication code written in S-Net. Our approach supports a component technology with flexible software reuse. No extension of the conventional language is required. The interface between S-Net and the application code is in terms of one additional library function. The application code is componentised and presented to S-Net as a set of components, called boxes, each encapsulating a single tuple-to-tuple function. Apart from the boxes defined using an external compute language, S-Net features two built-in boxes: one for network housekeeping and one for data-flow style synchronisation. Streaming network composition under S-Net is based on four network combinators, which have both deterministic and nondeterministic versions. Flexible software reuse is comprehensive, with the box interfaces and even the network structure being subject to subtyping. We propose an inheritance mechanism, named flow inheritance, that is specifically geared towards stream processing. The paper summarises the essential language constructs and type concepts and gives a short application example.

Parallel signal processing with S-Net

We argue that programming high-end stream-processing applications requires a form of coordination language that enables the designer to represent interactions between stream-processing functions asynchronously. We further argue that the level of abstraction that current programming tools engender should be drastically increased and present a coordination language and component technology that is suitable for that purpose. We demonstrate our approach on a real radar-data processing application from which we reuse all existing components and present speed-ups that we were able to achieve on contemporary multi-core hardware.

Coordinating Data Parallel SAC Programs with S-Net

We propose a two-layered approach for exploiting different forms of concurrency in complex systems: we specify computational components in our functional array language SAC, which exploits data parallel properties of array processing code. The declarative stream processing language S-Net is used to orchestrate the collaborative behaviour of these components in a streaming network. We illustrate our approach by a hybrid implementation of a sudoku puzzle solver as a representative for more complex search problems.

Reduction of nonlinear intrachannel effects by channel asymmetry in transmission lines with strong bit overlapping

We have examined the statistics of simulated bit-error rates in optical transmission systems with strong patterning effects and have found strong correlation between the probability of marks in a pseudorandom pattern and the error-free transmission distance. We discuss how a reduced density of marks can be achieved by preencoding optical data.

Message Driven Programming with S-Net: Methodology and Performance

Development and implementation of the coordination language S-NET has been reported previously. In this paper we apply the S-NET design methodology to a computer graphics problem. We demonstrate (i) how a complete separation of concerns can be achieved between algorithm engineering and concurrency engineering and (ii) that the S-NET implementation is quite capable of achieving performance that matches what can be achieved using low-level tools such as MPI. We find this remarkable as under S-NET communication, concurrency and synchronization are completely separated from algorithmic code. We argue that our approach delivers a flexible component technology which liberates application developers from the logistics of task and data management while at the same time making it unnecessary for a distributed computing professional to acquire detailed knowledge of the application area.

Information-Theory Analysis of Skewed Coding for Suppression of Pattern-Dependent Errors in Digital Communications

We present information-theory analysis of the tradeoff between bit-error rate improvement and the data-rate loss using skewed channel coding to suppress pattern-dependent errors in digital communications. Without loss of generality, we apply developed general theory to the particular example of a high-speed fiber communication system with a strong patterning effect

Implementing a numerical solution of the KPI equation using single assignment c: lessons and experiences

We report our experiences of programming in the functional language SaC[1] a numerical method for the KPI (Kadomtsev-Petiviashvili I) equation. KPI describes the propagation of nonlinear waves in a dispersive medium. It is an integro-differential, nonlinear equation with third-order derivatives, and so it presents a noticeable challenge in numerical solution, as well as being an important model for a range of topics in computational physics. The latter include: long internal waves in a density-stratified ocean, ion-acoustic waves in a plasma, acoustic waves on a crystal lattice, and more. Thus our solution of KPI in SaC represents an experience of solving a “real” problem using a single-assignment language and as such provides an insight into the kind of challenges and benefits that arise in using the functional paradigm in computational applications. The paper describes the structure and functionality of the program, discusses the features of functional programming that make it useful for the task in hand, and touches upon performance issues.

Teaching mathematical explanation through audiographic technology

Teaching mathematical explanation is now a National Curriculum requirement in the UK, but there is little support for teachers as to how this should be done. Written explanations are often seen as little more than stylised ways of presenting answers that have come to be accepted as social norms within the mathematics community. Teachers who wish to deviate from this view, however, or explore the teaching of multimodal explanations in mathematics, are left with little guidance as to how this might be achieved, and little support in practical issues such as record keeping, marking and classroom activities. Audiographic techniques are discussed as a suitable platform upon which such research and support for teaching and learning can be built.

An Active Organisation System for Customised, Secure Agent Discovery

The area of software agents has experienced an exponential growth during the past decade, and is now being given a further boost by the introduction of global distributed computing services, such as Globus and Legion. The focus of the research has gradually shifted from single agent architectures to multi-agent systems and agent societies. In a Grid computing environment, agents should be able to discover efficiently other agents based on the computational services they offer or their characteristics (agent discovery). Existing systems either ignore this issue or use simplistic organisation models, which act as passive “yellow pages” thus keeping the discovery process separate from the computation. In this paper it is argued that the agent discovery can be coupled with several aspects of the computation such as access control and customisation resulting in a better sharing, use and management of the information held by the agent discovery system. A novel architecture is presented in which discovery messages and discovery paths are mutable, active entities, which interact with each other as peers making the organisation system dynamic in nature. Queries traversing the system can be reformulated while at the same time the system itself can change depending on the nature and volume of the query traffic. Furthermore it is shown that the organisation nodes of the proposed architecture can serve as re-usable components for building more complex, composite nodes from existing ones.