Invariant Safety for Distributed Applications

We study a proof methodology for verifying the safety of data invariants of highly-available distributed applications that replicate state. The proof is (1) modular: one can reason about each individual operation separately, and (2) sequential: one can reason about a distributed application as if it were sequential. We automate the methodology and illustrate the use of the tool with a representative example.Comment: Workshop on Principles and Practice of Consistency for Distributed Data (PaPoC), Mar 2019, Dresden, Germany. https://novasys.di.fct.unl.pt/conferences/papoc19

Rhymes: a shared virtual memory system for non-coherent tiled many-core architectures

The rising core count per processor is pushing chip complexity to a level that hardware-based cache coherency protocols become too hard and costly to scale. We need new designs of many-core hardware and software other than traditional technologies to keep up with the ever-increasing scalability demands. The Intel Single-chip Cloud Computer (SCC) is a recent research processor exemplifying a new cluster-on-chip architecture which promotes a software-oriented approach instead of hardware support to implementing shared memory coherence. This paper presents a shared virtual memory (SVM) system, dubbed Rhymes, tailored to such a new processor kind of non-coherent and hybrid memory architectures. Rhymes features a two-way cache coherence protocol to enforce release consistency for pages allocated in shared physical memory (SPM) and scope consistency for pages in per-core private memory. It also supports page remapping on a per-core basis to boost data locality. We implement Rhymes on the SCC port of the Barrelfish OS. Experimental results show that our SVM outperforms the pure SPM approach used by Intel's software managed coherence (SMC) library by up to 12 times, with superlinear speedups (due to L2 cache effect) noted for applications with strong data reuse patterns.published_or_final_versio

The impact of organisational change on the role of the systems analyst

A major theme in the IS literature in recent years has been the dramatic impact of changes in technology and the business environment on the roles and skills of IS professionals. The British Computer Society (BCS) and other authorities suggest that roles are becoming broader and that demand is growing for a new breed of hybrid managers who possess a wide range of technical, business and organisational competences. Although it is recognised that there are constraints on developing hybrids, little research has been carried out on the nature of these constraints or on the impact of organisational change on IS roles. It was to fill this gap in the literature, and provide data that would be of value to practising managers, that the research presented in this thesis was undertaken. The main aims of the research were: (i) To explore the impact of change on the roles of a group of systems analysts; (ii) to examine the systems analysts' perception of the effects of change on their role and (iii) to determine whether there were any factors impeding the hybridisation of the analyst's role. Analysts were selected as the focal group for many reasons but mainly that their role requires hybrid competences and they would therefore be a good group to examine the strength of the forces for / against change. The decision to focus on the analysts' perceptions was to gauge individual reactions to change. Since the individual's perception of events is likely to influence their behaviour, it was reasoned that if the analysts' perceived change to have negative consequences, their attitude may be a constraint on hybridisation and on organisational change. It would therefore be of practical value to gain a clearer understanding of the analysts' view of the change process. The case study approach was used to examine the impact of change on the analyst's role. Although other methods could have been used, the case study would permit detailed analysis of the process of organisational change and provide an effective means of accessing the analysts' perceptions of the impact of change. The research was carried out in five organisations: three in the financial services sector and two in the retail sector. The decision to base the research in a number of companies and different sectors was to examine differences between organisations and to illuminate the impact of contextual factors. Financial services and retail organisations were considered an appropriate choice for the research because they tend to rely heavily on IT and have been subject to very rapid sectoral change over the last few years. The BCS maintains that these are the conditions in which hybrid managers are most likely to emerge. If the organisations selected fulfilled the Society's criteria and the roles of the analysts were technically defined, this would point to constraints on hybridisation. To analyse the impact of organisational change on roles a theoretical framework was developed which identified the factors that influence roles and explained the dynamics of the change process. A distinction was drawn between factors in the outer context (macro-environmental, sectoral and occupational factors) and the inner context (the organisation and individual role encumbents). These factors were reconfigured in terms of Lewin's fields of force model to suggest how organisational change and change in roles may come about. Thirty-five systems analysts took part in the research. The impact of change was examined over a period of six years (1989-1995), the average length of the analysts' tenure in the participating companies. Data was collected using a variety of methods, including a self-administered questionnaire, interviews with analysts and their IS and Personnel Managers and examination of company documents. In spite of the dramatic changes that had taken place in the case study organisations, the findings reveal that three continued to define the analyst's role in technical terms. Two had broadened the roles of the analysts but there were still constraints on the extent of change. These constraints included the structure and culture of the organisation, the strategies for managing the IS department/division, the emergence of new occupational groups and the analyst's own orientation to their role. The research suggests that the impact of change on the analyst's role may vary between organisations and reflect the influence of contextual factors; that dramatic organisational change does not necessarily create conditions that are conducive to developing hybrids and that there may be significant constraints on bringing about change in the analyst's role. The thesis provides empirical data on the impact of change on roles and helps to explain some of the reasons companies may be experiencing difficulty developing hybrids. Although it helps to fill a gap in the IS literature, it is suggested that more contextual/interpretive studies are needed on the constraints on hybridisation in different organisations and on different occupational groups

A fault-tolerant multiprocessor architecture for aircraft, volume 1

A fault-tolerant multiprocessor architecture is reported. This architecture, together with a comprehensive information system architecture, has important potential for future aircraft applications. A preliminary definition and assessment of a suitable multiprocessor architecture for such applications is developed

Introductory programming: a systematic literature review

As computing becomes a mainstream discipline embedded in the school curriculum and acts as an enabler for an increasing range of academic disciplines in higher education, the literature on introductory programming is growing. Although there have been several reviews that focus on specific aspects of introductory programming, there has been no broad overview of the literature exploring recent trends across the breadth of introductory programming. This paper is the report of an ITiCSE working group that conducted a systematic review in order to gain an overview of the introductory programming literature. Partitioning the literature into papers addressing the student, teaching, the curriculum, and assessment, we explore trends, highlight advances in knowledge over the past 15 years, and indicate possible directions for future research

Software tools for the cognitive development of autonomous robots

Robotic systems are evolving towards higher degrees of autonomy. This paper reviews the cognitive tools available nowadays for the fulfilment of abstract or long-term goals as well as for learning and modifying their behaviour.Peer ReviewedPostprint (author's final draft