An Analysis of Composability and Composition Anomalies

The separation of concerns principle aims at decomposing a given design problem into concerns that are mapped to multiple independent software modules. The application of this principle eases the composition of the concerns and as such supports composability. Unfortunately, a clean separation (and composition of concerns) at the design level does not always imply the composability of the concerns at the implementation level. The composability might be reduced due to limitations of the implementation abstractions and composition mechanisms. The paper introduces the notion of composition anomaly to describe a general set of unexpected composition problems that arise when mapping design concerns to implementation concerns. To distinguish composition anomalies from other composition problems the requirements for composability at the design level is provided. The ideas are illustrated for a distributed newsgroup system

Towards a taxonomy of distributed-object models

Different ideas about object-orientation and distributed computing have resulted in a large number of distributed-object models. Use of the same terminology with different meanings makes these models hard to compare. What is currently missing is a framework for describing object models which can be used to compare and classify them. An attempt at defining such a framework is presented in this paper.

A Programming Environment Evaluation Methodology for Object-Oriented Systems

The object-oriented design strategy as both a problem decomposition and system development paradigm has made impressive inroads into the various areas of the computing sciences. Substantial development productivity improvements have been demonstrated in areas ranging from artificial intelligence to user interface design. However, there has been very little progress in the formal characterization of these productivity improvements and in the identification of the underlying cognitive mechanisms. The development and validation of models and metrics of this sort require large amounts of systematically-gathered structural and productivity data. There has, however, been a notable lack of systematically-gathered information on these development environments. A large part of this problem is attributable to the lack of a systematic programming environment evaluation methodology that is appropriate to the evaluation of object-oriented systems

The object-oriented paradigm as an implementation of systems theory in IS

Classical General Systems Theory (GST) is rich with fundamental concepts relating to the explanation of how systems behave and operate. The new concept of object-oriented techniques and methodologies was found to be closely aligned with most of the fundamental theories of GST. This article presents these alignments and similarities and clearly shows that object-oriented techniques provide a better fit to GST than older design methodologies

On Agent-Based Software Engineering

Agent-based computing represents an exciting new synthesis both for Artificial Intelligence (AI) and, more generally, Computer Science. It has the potential to significantly improve the theory and the practice of modeling, designing, and implementing computer systems. Yet, to date, there has been little systematic analysis of what makes the agent-based approach such an appealing and powerful computational model. Moreover, even less effort has been devoted to discussing the inherent disadvantages that stem from adopting an agent-oriented view. Here both sets of issues are explored. The standpoint of this analysis is the role of agent-based software in solving complex, real-world problems. In particular, it will be argued that the development of robust and scalable software systems requires autonomous agents that can complete their objectives while situated in a dynamic and uncertain environment, that can engage in rich, high-level social interactions, and that can operate within flexible organisational structures

Computing infrastructure issues in distributed communications systems : a survey of operating system transport system architectures

The performance of distributed applications (such as file transfer, remote login, tele-conferencing, full-motion video, and scientific visualization) is influenced by several factors that interact in complex ways. In particular, application performance is significantly affected both by communication infrastructure factors and computing infrastructure factors. Several communication infrastructure factors include channel speed, bit-error rate, and congestion at intermediate switching nodes. Computing infrastructure factors include (among other things) both protocol processing activities (such as connection management, flow control, error detection, and retransmission) and general operating system factors (such as memory latency, CPU speed, interrupt and context switching overhead, process architecture, and message buffering). Due to a several orders of magnitude increase in network channel speed and an increase in application diversity, performance bottlenecks are shifting from the network factors to the transport system factors.This paper defines an abstraction called an "Operating System Transport System Architecture" (OSTSA) that is used to classify the major components and services in the computing infrastructure. End-to-end network protocols such as TCP, TP4, VMTP, XTP, and Delta-t typically run on general-purpose computers, where they utilize various operating system resources such as processors, virtual memory, and network controllers. The OSTSA provides services that integrate these resources to support distributed applications running on local and wide area networks.A taxonomy is presented to evaluate OSTSAs in terms of their support for protocol processing activities. We use this taxonomy to compare and contrast five general-purpose commercial and experimental operating systems including System V UNIX, BSD UNIX, the x-kernel, Choices, and Xinu