A timeband framework for modelling real-time systems

Complex real-time systems must integrate physical processes with digital control, human operation and organisational structures. New scientific foundations are required for specifying, designing and implementing these systems. One key challenge is to cope with the wide range of time scales and dynamics inherent in such systems. To exploit the unique properties of time, with the aim of producing more dependable computer-based systems, it is desirable to explicitly identify distinct time bands in which the system is situated. Such a framework enables the temporal properties and associated dynamic behaviour of existing systems to be described and the requirements for new or modified systems to be specified. A system model based on a finite set of distinct time bands is motivated and developed in this paper

Deriving specifications of control programs for cyber physical systems

Cyber Physical Systems (CPS) exist in a physical environment and comprise both physical components and a control program. Physical components are inherently liable to failure and yet an overall CPS is required to operate safely, reliably and cost effectively. This paper proposes a framework for deriving the specification of the software control component of a CPS from an understanding of the behaviour required of the overall system in its physical environment. The two key elements of this framework are (i) an extension to the use of rely/guarantee conditions to allow specifications to be obtained systematically from requirements (as expressed in terms of the required behaviour in the environment) and nested assumptions (about the physical components of the CPS); and (ii) the use of time bands to record the temporal properties required of the CPS at a number of different granularities. The key contribution is in combining these ideas; using time bands overcomes a significant drawback in earlier work. The paper also addresses the means by which the reliability of a CPS can be addressed by challenging each rely condition in the derived specification and, where appropriate, improve robustness and/or define weaker guarantees that can be delivered with respect to the corresponding weaker rely conditions

Opportunities for managing peak train travel demand: a Melbourne pilot study

Melbourne, like many large cities around the world, experiences significant peak congestion on its public transport network. Demand for services in peak times is a key driver of investment in new rolling stock and infrastructure. A way of delaying these significant investments is to better utilize current available resources in non-peak times, by spreading out peak demand over a wider time period.This study used an online survey methodology to investigate the propensity of peak period train passengers commuting for work on Melbourne‟s Pakenham line to shift out of peak travel times to access a better price, service frequency, stopping pattern and train conditions. The main methodology was two Discrete Choice Model exercises (one morning-peak and one afternoon-peak) which systematically varied time of travel, price and service attributes to model customer behaviour under various scenarios.The results support the view that demand can be influenced by price and service attributes, and support the development of detailed business cases for reducing peak demand. Implications are discussed, as well as the challenges in converting these customer behaviour predictions into workable timetables, and in accurately costing the benefits of delays in investments in new rolling stock and infrastructure

Formalised responsibility modelling for automated socio-technical systems analysis

Modelling the structure of social-technical systems as a basis for informing software system design is a difficult compromise. Formal methods struggle to capture the scale and complexity of the heterogeneous organisations that use technical systems. Conversely, informal approaches lack the rigour needed to inform the software design and construction process or enable automated analysis. We revisit the concept of responsibility modelling, which models social technical systems as a collection of actors who discharge their responsibilities, whilst using and producing resources in the process. In this thesis responsibility modelling is formalised as a structured approach for socio-technical system specification and modelling, with well-defined semantics and support for automated structure and validity analysis. We provide structured definitions for entity types and relations, and define the semantics of delegation and dependency. A constraint logic is introduced, providing simple specification of complex interactions between entities. Additionally, we introduce the ability to explicitly model uncertainty. To support this formalism, we present a new software toolkit that supports modelling and automatic analysis of responsibility models in both graphical and textual form. The new methodology is validated by applying it to case studies across different problem domains. A study of nuclear power station emergency planning is validated by comparison to a similar study performed with earlier forms of responsibility modelling, and a study of the TCAS mid-air collision avoidance system is validated by evaluation with domain experts. Additionally, we perform an explorative study of responsibility modelling understanding and applicability through a qualitative study of modellers

Proceedings of the 11th Overture Workshop

The 11th Overture Workshop was held in Aarhus, Denmark on Wed/Thu 28–29th Au- gust 2013. It was the 11th workshop in the current series focusing on the Vienna De- velopment Method (VDM) and particularly its community-based tools development project, Overture (http://www.overturetool.org/), and related projects such as COMPASS(http://www.compass-research.eu/) and DESTECS (http://www.destecs.org). Invited talks were given by Yves Ledru and Joe Kiniry. The workshop attracted 25 participants representing 10 nationalities. The goal of the workshop was to provide a forum to present new ideas, to identify and encourage new collaborative research, and to foster current strands of work towards publication in the mainstream conferences and journals. The Overture initiative held its first workshop at FM’05. Workshops were held subsequently at FM’06, FM’08 and FM’09, FM’11, FM’12 and in between

A double-edged sword : the minimum wage and agrarian labour in the Eastern Cape, South Africa, 2003–2014

Statutory wage setting and the extension of labour laws to the South African agrarian labour market are path-breaking events that altered the unilateral power which agrarian employers had, under apartheid, to set low wages and harsh employment conditions. Yet, economic sociologists have shown little interest in the agrarian minimum wage in South Africa. Consequently, little to no sociological perspectives are available on the way in which statutory wages shape the setting of actual agrarian wages, employment conditions, labour relations and working and living conditions. At the same time, economic sociology’s neglect of agrarian minimum wages perpetuates the dominance of economics in minimum wage research, as well as the narrow cost-benefit analysis, and firm and employer-centric focus, deployed by both opponents of minimum wages in the neoclassical economics camp and supporters in the heterodox economics camp. The firm-centric focus also applies to the few labour relations scholars who focus on minimum wages. As a result, a wide body of empirical information is available and concentrated in the Global North, on low-waged, urban-based firms’ employment and labour relations strategies with the occasioning of minimum wage laws, with scant to non-existing information on rural-based workers’ experiences in the Global South, at least in the case of South Africa. This thesis addresses the lacuna in existing research, specifically by concentrating on agrarian workers’ narratives of the outcomes of minimum wages on actual wages and conditions, and experiences at the site of production and in the sphere of expanded social reproduction. The conceptual framework of the thesis is rooted in a critical realist meta-theory which directs inquiry towards the search for underlying causes of events with a sensitivity to the interaction of structure and agency, so as to develop explanations of events, which in turn encourage emancipatory thought and praxis. Within this framework, a political economy perspective of the agrarian minimum wage is charted, founded on an inter-disciplinary approach that incorporates economic sociology perspectives, which view markets as socio-political constructs, alongside a Marxist analysis of wages and the distinction between the value of labour and the value of labour power. Also relevant are segmentation labour market models where the focus is on segmentation in labour supply, demand and regulation, and institutional economics that highlights labour’s weak bargaining power in low-waged labour markets. Based on this analytical perspective, the South African agrarian minimum wage is seen as a necessary intervention stemming from post-apartheid uneven neoliberal restructuring processes, to address extremely low agrarian wages that pose threats to the ongoing generation of agrarian labour power. Low agrarian wages are located in unequal power relations in the workplace and are embedded in the totality of the low-waged agrarian labour market, composed of particular features in the supply-side of the labour market (the sphere of social reproduction of labour), the demand-side of the labour market (the site of production), and the forces of regulation (the labour relations regime). The thesis explores new ways of conceptualising minimum wages in the South African context, placing emphasis on the local agrarian labour market, and it highlights the agency of agrarian labour by revealing their struggles, working life and living conditions. In so doing, the research expands inquiry beyond economic “impact” at the level of the firm/employer to examine: (a) workers’ employment trends before and after the minimum wage was introduced, (b) the extent of changes in working and living conditions and labour relations, (c) the scope for workers in animating changes and their struggles and challenges, and (d) shifts in actual wages in relation to prescribed wage rates. Focussing on the aforementioned aspects represents an attempt in this thesis to build on themes, raised in heterodox economics studies, of minimum wages and their relationship to the social devaluation of low-waged work, inequalities in bargaining power, and justice. Based on a stratified sample of workers that included, among other variables, sex, geographical area and agricultural sub-sectors, original data was collected through 52 in-depth interviews, two focus group interviews (comprised of 10 workers), and 501 surveyed workers. The research did not find widespread job losses when minimum wages were introduced, as per neoclassical economics’ predictions. Nor did it find transitions from low- to high-road approaches in employment strategies and labour relations, as claimed by certain heterodox economists. Instead, the findings at the sites of production corroborate the uneven, mixed and contradictory findings of applied heterodox minimum wage studies on employment strategies, labour relations and wage settings. In this light, it is concluded that the agrarian minimum wage had layered outcomes for workers based on key findings, which include: (a) the minimum wage became the maximum wage as actual wages increased and clustered at the prescribed wage rate; (b) a level of gender wage parity close to the level of the prevailing prescribed minimum wage was found, but an overall gendered pattern to low-waged employment surfaced and manifested differently at sub-sector and enterprise levels; (c) though no changes were found in the way work was organised and how workers executed their tasks alongside no fundamental changes in the social relations of production, statutory minimum wages and limitations on working hours did reduce the hours of work and the existence of unpaid overtime work in certain sub-sectors such as livestock and dairy workplaces, through worker and employer initiatives (yet, at the same time, work intensification in compressed working hours appeared in the sample in other worksites, for example citrus workplaces); (d) authoritarian labour relations existed in varying depths and forms, based on sub-sector and enterprise characteristics, which shaped the propensity and scope for worker action; and (e) the layered outcomes of the agrarian minimum wage were felt at the site of social reproduction, where it brought a measure of relief for sampled workers; however, it was chronically inadequate to allow workers to meet their subsistence needs comprehensively. The research findings also highlight sub-sectoral complexities in changing employment and labour relations strategies from low- to high-road approaches in the agrarian sector. The layered outcomes of minimum wages for agrarian workers stems from the combined and uneven amalgamation of pre-existing and new conditions and relations consequent to neoliberalising processes in the agrarian political economy as well as the low minimum wage-setting. The thesis thus argues that the mixed outcomes reflect the layered character of the minimum wage as a conversion factor, which in turn equates to a layered notion of justice. This is because, on the one hand, the minimum wage ameliorates the plight of agrarian labour but, on the other hand, and given the bulwark of authoritarianism, pre-existing conditions and neoliberalising processes, the collective vulnerabilities in the agrarian labour market have expanded and may be intensifying. The agrarian minimum wage acts as a double-edged sword in contexts of mixed and layered outcomes for agrarian labour. A layered perspective of the conversion factor of a minimum wage exposes the possibilities and limitations of statutory wages as a conversion factor, based on context, and identifies the limits and possibilities for worker mobilisation and action. In the case of this research, the agrarian minimum wage deals in limited fashion with the value of labour power because of the initial and subsequent low settings; the minimum wage does not deal with class exploitation and the value of labour, although it sets the frame for instigating basic labour standards. The implications of a layered conversion potential of low minimum wage-settings are profound for conceptualising, theorising and researching the link between statutory wages and justice, with respect to the value of labour power and the value of labour. Future research on the minimum wage based on a Marxist reading of wages and located in real labour markets, strengthens heterodox approaches by deepening theories on the relationship between statutory wages, justice and production.Thesis (PhD) -- Faculty of Humanities, Department of Sociology, 202

The use and development of geographical information systems (GIS) and spatial modelling for educational planning

Since the passing of the 1988 Education Reform Act British education, particularly at a secondary level, has been transformed. The changes enacted in this and subsequent legislation have opened up state-provided education to a market-oriented system which is led more by the preferences of parents than the dictation of local or national planners. This means that local authorities and other providers of education have been left in a situation where they are relatively powerless to provide adequate schooling in a proactive manner. It is also the case that there is a danger of a 'two-tier' education system developing whereby the better-informed middle classes are served by high achieving schools and less advantaged pupils are left to fill inner city 'sink' schools which cannot provide them with the same educational chances due to lower resource levels. This thesis presents a feasibility study of a variety of techniques drawn from academic and applied geography which can be utilised by such planners in order to better target the resources available to them and improve their reactions to the vagaries of the market. These tools concentrate on geographical information systems (GIS) and spatial modelling techniques. Although both of these sets of techniques have for many years been applied in other areas, including within local Government, they have yet to permeate to a decision-making level in education planning. Thus the time is ripe for their wider dissemination and application in this area. Several examples of the possible uses of GIS are given, using real data for Leeds schools and pupils. Various types of spatial model are described and the most appropriate are calibrated and applied using the same Leeds data. The thesis concludes that the benefits of modelling techniques for planners at all scales, from individual schools to national Government, could be enormous. Through the application of these tools planners will be better placed to provide an education service which caters for all pupils within it. However, there are caveats regarding the requirement for further research into improving model performance and ensuring that output is sufficiently user-friendly

A situated method for modelling and analysing the efficiency of cognitive activity during the radiology reporting workflow using eye-tracking

The success of modern medical imaging systems has created a data overload problem, where an ever-increasing number of examinations, generate more images per study, which all need to be evaluated by radiologists or other reporting practitioners. This operational bottleneck hasthe potentialto create fatigue and burnout due to the high mental workload that is required to keep up with the demand. The focus of this problem centres around the cognitive complexity of the radiology reporting workflow, and the associated workstation interactions involved in diagnostic report generation. There has been a significant body of work evaluating the behaviour of radiologists using controlled laboratory-based techniques, but these non-naturalistic studies fail to address the highly context dependant nature of the radiology reporting workflow. For example, the early eye-tracking work of Charmody et al; the psychometric studies by Krupinksi et al; and also the workstation interaction evaluations of Moise et al; whilst highly principled, can be all be questioned on the grounds of ecological validity and authenticity. This thesis asserts that the only way to truly understand and resolve the radiology data overload problem, is by developing a situated method for observing the reporting workflow that can evaluate the behaviours of the reporting clinicians in relation to their authentic reporting context. To this end, this study has set out to develop a new approach for observing and analysing the cognitive activities of the reporters relative to the demands of their genuine working environment, and supported through the application of a Critical Realist’s perspective to naturalistic workplace observations. This goal was achieved through the development of four key project deliverables: • An in-depth exploratory study of the radiology overload problem based on an extensive literature review and situated observations of authentic reporting workflows. • A descriptive hierarchical activity modelof the reporting workflow that can be understood by both clinicians, application designers and researchers. • A generalised methodology and research protocolfor conducting situated observations of the radiology reporting workflow, using an analysis based on the process tracing of sequencesof Object Related Actions, captured with eye-tracking and multimodal recordings. • A set of case studies demonstrating the applicability of the research protocol involving 5 Radiology Consultants, 2 Radiology Registrars and one Reporting Radiographer at a single NHS Hospital within the UK. The final workflow evaluation of the case studies demonstrated that activities such as error correction, and the collection of supporting radiological information from previous studies is complex, time consuming and cognitively demanding. These types of activities are characterised by long, low utility actions that correspond to what Kahneman refers to as “Thinking Slow”. Also, the participants appeared to be self-optimising their workflow via a sparse use of complex functionality and system tools. From these observations, the author recommends that any intervention that can reduce the number and the duration of the object related actions used to produce radiology reports, will reduce cognitive load, increase overall efficiency, and go some way to alleviate the data overload problem. 4 This study establishes a new set of situated techniques that are able to capture and quantify the complex dynamicactivities that make up the radiology reporting workflow. Itis hoped that the ability to distil usefuland impactful insightsfrom the user’s workstation behaviours can be used as the basis for further development in the area of workflow analysis and redesign, which will ultimately improve the working lives of Radiologists and other Reporting Clinicians. Lastly, the generic nature of these techniques make them amenable for use within any type of complex sociotechnical human factors study related to the cognitive efficiency of the user

Understanding the Relationship Between Capacity Utilisation and Performance and the Implications for the Pricing of Congested Rail Networks.

There is a growing demand for rail travel in this country which is difficult to satisfy. The result is increased congestion on Britain’s railways. One feature of rail infrastructure congestion is a direct link between capacity utilisation and reactionary delay. The latter is the secondary delay that an already late train causes to a following train. This thesis re-examines the relationship between capacity utilisation and performance (as expressed by the level of reactionary delay). It compares the effectiveness of the standard measure of capacity utilisation in Britain (the Capacity Utilisation Index or CUI) with amongst others a measure developed in the Netherlands (the Heterogeneity measure or HET) which uses a radically different approach. The analysis presented in this thesis finds that HET which measures how capacity is used through the spacing of trains, is a more effective predictor of the levels of reactionary delay than CUI which simply measures how much capacity is used. In both cases though, an exponential relationship between capacity utilisation and reactionary delay is preferred, reinforcing the work of previous researchers. In 2002 a congestion charge, called The Capacity Charge, was introduced in Britain. The idea was to encourage the Infrastructure Owner (now known as Network Rail) to accommodate more traffic whilst working with train operators to optimise capacity utilisation on the network. The Capacity Charge is based on the relationship between CUI and reactionary delay. However, this thesis shows that HET based tariffs would charge more for congestion than CUI based tariffs. In addition there is a greater differential between peak and off-peak charges. One conclusion is that CUI undercharges for congestion due to its failure to account for the impact of train ‘bunching’