Showing papers in "CTIT technical reports series in 2002"

On Architectural Support for Behaviour Refinement in Distributed Systems Design

Abstract: During the top-down design of distributed systems, abstract designs have to be replaced by more concrete designs, which add details that define how these systems can be implemented using available building blocks. Behaviour refinement is a design operation in which abstract behaviours are replaced by more concrete behaviours. Methods that guide and enforce the correctness of these replacements are necessary. This paper presents a set of methods to perform behaviour refinement, based on a careful consideration of the architectural concepts of action and causality relation. Correctness is enforced by validation of the conformance relation between an abstract and a concrete behaviour. Rules are provided to determine whether a concrete behaviour conforms to an abstract behaviour.

Towards a Strongly Typed Functional Operating System

Abstract: In this paper, we present Famke. It is a prototype implementation of a strongly typed operating system written in Clean. Famke enables the creation and management of independent distributed Clean processes on a network of workstations. It uses Clean's dynamic type system and its dynamic linker to communicate values of any type, e.g. data, closures, and functions (i.e. compiled code), between running applications in a type safe way. Mobile processes can be implemented using Famke's ability to communicate functions. We have built an interactive shell on top of Famke that enables user interaction. The shell uses a functional-style command language that allows construction of new processes, and it type checks the command line before executing it. Famke's type safe run-time extensibility makes it a strongly typed operating system that can be tailored to a given situation.

Separating distribution policies in a shared data space system

Abstract: To more fully exploit its benefits, the principle of separation of concerns should be built into the methods of designing systems as well as into the techniques that we use for implementation. We argue that for distributed applications, separating concerns should be supported by the middleware on which the applications are executed. In particular, we argue that the middleware should provide the proper mechanisms to enforce application-specific policies for different concerns. Interweaving of policies should take place at run time such that it becomes possible to change them without the need for recompiling the application source code. To illustrate that this approach is principally feasible, we present a design for a middleware based on the shared data space paradigm. Here distribution is taken as an example of a concern that can be treated separately from other concerns and transparently to applications. We present a case study that shows how we can vary the distribution policy for an application. The case study shows a trade-off between the use of bandwidth versus the speed of message delivery.

An approach to the construction of flexible B2B E-contracting processes

Abstract: In business-to-business relations, contracts serve both as a protection mechanism of trading parties, as well as a prescription document for activities to be executed by them. The processes of contract establishment and its enactment are often expensive and time-consuming. E-contracting aims at improving the efficiency and effectiveness of the contracting process. Additionally, it offers new opportunities to the contracting parties, e.g. micro-contracting. For the design of an information system for support of e-contracting, a clear description of the e-contracting processes is required. In this report, we introduce a process model for flexible business-to-business e-contracting. To separate concerns, we distinguish structured function and communication perspectives of e-contracting processes supplemented with consistency rules. Using the defined model we propose an approach for elaboration of concrete e-contracting process specifications and their implementation in real-life business scenarios. The approach is a basis for complete functional e-contracting process specifications, with coherent communication between contracting parties and coupling between the internal and external activities of a company.

A selectivity model for fragmented relations: Evaluated for different standard data distributions

Abstract: In the estimation of selectivity, many models assume that data is uniformly distributed, which is not true for many applications. In this paper, we discuss a generalized selectivity model, the so-called lαβ-model which is independent of the data distribution. The model predicts the fraction of a relation that should be selected in order to process a query. We have evaluated this model for different data distributions in order to determine the accuracy of this model. Data distributions that have been considered are the uniform distribution, the normal distribution, the exponential distribution, Pearson’s distribution, and Zipf’s distribution. From our experiments, it appears that the lαβ-model predicts the selectivity well, especially for the skewed distributions. Applying the lαβ-model on different fragment sizes of a relation yields quite acceptable selectivity values as well.

Decomposing modal logic

Abstract: We provide a detailed analysis of very weak fragments of modal logic. Our fragments lack connectives that introduce non-determinism and they feature restrictions on the modal operators, which may lead to substantial reductions in complexity. Our main result is a general game-based characterization of the expressive power of our fragments over the class of finite structures.

Dynamic Values Need Polytypic Functions - Draft -

Abstract: To do.