Panayiotis Periorellis

Organisational Failures in Dependable Collaborative Enterprise Systems

In this paper we attempt to classify organizational failures that can occur during the integration process of autonomous systems. The paper reports on ongoing research in the area of systems integration. Our purpose is to provide a taxonomy of organizational failures, so that there is a basis for analyzing some of the possible organizational failure modes resulting from putting together two organizational systems, each with its own purpose in its own organizational context, to make a new Dependable System of Systems. It thus provides a way of examining some new emergent failure modes. It also points out possible failure modes that, because they are organizational, cannot be prevented or tolerated at the level of the individual technical systems or the technical system that brings them together.

Using co-ordinated atomic actions for building complex Web applications: a learning experience

This paper discusses some of the typical characteristics of modern Web applications and analyses some of the problems the developers of such systems have to face. One of such types of applications is integrated Web application, i.e. application that integrates several independent Web services. The paper focuses on providing software fault tolerance for such systems. The solution we put forward employs the concept of co-ordinated atomic (CA) actions for structuring such applications and for providing fault tolerance using exception handling. The paper discusses important design and implementation decisions we have made while developing a travel agency (TA) case study and attempts to generalize them to allow CA actions to be easily applied for building dependable Web applications.

Exploiting the TTL Rule in Unstructured Peer-to-Peer Networks

Peer-to-peer networks exist with the volunteering cooperation of various entities on the Internet. Their self-structure nature has the important characteristic that they make no use of central entities to run as coordinators and the benefits of this cooperation can be enjoyed equally by all the members of the community with the assumption that they all make right use of the protocol. In this study we examine what the consequences on the community are in the case of existence of misbehaving nodes which can abuse the network resources for their personal benefit and we also analyze the cost and the benefit of some proposed solution that could be used in order to bring into account the above problem

A policy for electing super-nodes in unstructured p2p networks

Unstructured P2P networks, despite having good characteristics such as the nonexistence of a single point of failure, the high levels of anonymity in the search operations and the exemplary dependability, have been found to be much less scalable than first expected. The flooding protocol, which is used for the discovery of peers and for the main operation of searching, seems to be responsible for this weakness. The adoption of some major improvements, such as the distinction between Leaf-nodes and Ultra-Peers, has partially overcome the scalability problems, but there is still a need for further optimization. Our proposed idea, aims to improve the effectiveness of the hierarchical scheme by applying some new criteria in the selection of potentially promotable nodes.

Structured Handling of Online Interface Upgrades in Integrating Dependable Systems of Systems

The integration of complex systems out of existing systems is an active area of research and development. There are many practical situations in which the interfaces of the component systems, for example belonging to separate organisations, are changed dynamically and without notification. Usually systems of system (SoS) developers deal with such situations off-line causing considerable downtime and undermining the quality of the service that SoSs are delivering [Romanovsky & Smith 2002]. In this paper we propose an approach to on-line handling such upgrades in a structured and disciplined fashion. All interface changes are viewed as abnormal events and general fault tolerance mechanisms (exception handling, in particular) are applied to dealing with them. The paper outlines general ways of detecting such interface upgrades and recovering after them. An Internet Travel Agency is used as a case study throughout the paper. An implementation demonstrating how the general approach proposed can be applied for dealing with some of the possible interface upgrades within this case study is discussed.

Modelling dynamic networks: advantages and limitations of the O-O approach

The paper reports on ongoing research into the area of enterprise modelling. We have concluded so far that most enterprise models are static representations of enterprises that are expressed using diagrammatic schemes or computing simulation techniques. Their life cycle is usually very brief as they fail to adapt to changes that take place in an enterprises dynamic environment. On the other hand, enterprise models are directed to specific business junctions, omitting the fact that relationships between various enterprise agents affect their operations. The paper reports on our attempt to provide a framework for assessing the impact of change that is caused by the formulation or deletion of relationships between agents, on a wider environment. The framework is being tested on supply chains. For the sake of consistency the authors refer to the automotive sector throughout the paper.