Learning Recursive Functions From Approximations

This article investigates algorithmic learning, in the limit, of correct programs for recursive functionsffrom both input/output examples offand several interesting varieties ofapproximateadditional (algorithmic) information aboutf. Specifically considered, as such approximate additional information aboutf, are Rose\u27s frequency computations forfand several natural generalizations from the literature, each generalization involving programs for restricted trees of recursive functions which havefas a branch. Considered as the types of trees are those with bounded variation, bounded width, and bounded rank. For the case of learning final correct programs for recursive functions, EX-learning, where the additional information involves frequency computations, an insightful and interestingly complex combinatorial characterization of learning power is presented as a function of the frequency parameters. For EX-learning (as well as for BC-learning, where a finalsequenceof correct programs is learned), for the cases of providing the types of additional information considered in this paper, the maximal probability is determined such that the entire class of recursive functions is learnable with that probability

Retrieval for Extremely Long Queries and Documents with RPRS: a Highly Efficient and Effective Transformer-based Re-Ranker

Retrieval with extremely long queries and documents is a well-known and challenging task in information retrieval and is commonly known as Query-by-Document (QBD) retrieval. Specifically designed Transformer models that can handle long input sequences have not shown high effectiveness in QBD tasks in previous work. We propose a Re-Ranker based on the novel Proportional Relevance Score (RPRS) to compute the relevance score between a query and the top-k candidate documents. Our extensive evaluation shows RPRS obtains significantly better results than the state-of-the-art models on five different datasets. Furthermore, RPRS is highly efficient since all documents can be pre-processed, embedded, and indexed before query time which gives our re-ranker the advantage of having a complexity of O(N) where N is the total number of sentences in the query and candidate documents. Furthermore, our method solves the problem of the low-resource training in QBD retrieval tasks as it does not need large amounts of training data, and has only three parameters with a limited range that can be optimized with a grid search even if a small amount of labeled data is available. Our detailed analysis shows that RPRS benefits from covering the full length of candidate documents and queries.Comment: Accepted at ACM Transactions on Information Systems (ACM TOIS journal

Full coverage displays for non-immersive applications

Full Coverage Displays (FCDs), which cover the interior surface of a room with display pixels, can create novel user interfaces taking advantage of natural aspects of human perception and memory which we make use of in our everyday lives. However, past research has generally focused on FCDs for immersive experiences, the required hardware is generally prohibitively expensive for the average potential user, configuration is complicated for developers and end users, and building applications which conform to the room layout is often difficult. The goals of this thesis are: to create an affordable, easy to use (for developers and end users) FCD toolkit for non-immersive applications; to establish efficient pointing techniques in FCD environments; and to explore suitable ways to direct attention to out-of-view targets in FCDs. In this thesis I initially present and evaluate my own "ASPECTA Toolkit" which was designed to meet the above requirements. Users during the main evaluation were generally positive about their experiences, all completing the task in less than three hours. Further evaluation was carried out through interviews with researchers who used ASPECTA in their own work. These revealed similarly positive results, with feedback from users driving improvements to the toolkit. For my exploration into pointing techniques, Mouse and Ray-Cast approaches were chosen as most appropriate for FCDs. An evaluation showed that the Ray-Cast approach was fastest overall, while a mouse-based approach showed a small advantage in the front hemisphere of the room. For attention redirection I implemented and evaluated a set of four visual techniques. The results suggest that techniques which are static and lead all the way to the target may have an advantage and that the cognitive processing time of a technique is an important consideration."This work was supported by the EPSRC (grant number EP/L505079/1) and SurfNet (NSERC)." - Acknowledgement

Value-added and sustainability reporting : leveraging on conventional accounting practices for accountability and information decision usefulness – a case study of South Africa

Following the emerging and increasing interest in value-added and sustainability reporting, countries like South Africa have enhanced their corporate sustainability disclosures (CSDs) through the use of acceptable value-added statements (VAS) and related metrics in their annual reports. Listed companies on the JSE Ltd have either produced a VAS, Sustainable Development Report (SDRs) or related CSDs by leveraging on existing reporting frameworks to meet the information user needs of the wider stakeholders. This thesis used a mixed method approach to examine the reasonable acceptability of the VAS as an ideal value added report by corporate organisations to meet the information user needs of the wider stakeholder groups. Additionally, this thesis sought to understand the detailed Sustainability and Value – Added Reporting (VAR) practices of corporate organisations by using the South African context as a case study. The quantitative approach revealed that there is a growing trend in the amount and volume of value-added and sustainability reports produced by listed firms in South Africa. It further revealed the increasing appetite by corporate entities to include infographics and supporting narratives to explain the sustainability and value added practices of the companies with the aim of gaining and maintaining legitimacy in their business environments. The qualitative findings suggest that value-added and sustainability reporting converge with and diverge from each other which requires a clearer delineation of these practices. Furthermore, the qualitative findings suggest that harmonizing the various sustainability reporting standards into common canons could take a while due to the consistently changing dynamics of sustainable development programmes. However, there is the need to effectively assure (audit) these value-added and sustainability programmes of corporate entities and possibly align them to generally acceptable reporting frameworks such as the UN System of National Accounting in order to unearth more items of values. In doing so, corporate value-added practices and sustainability programmes will go a long way to help the wider stakeholders make informed and useful decisions. The research concluded that in order for corporate entities in emerging economies like South Africa to gain the legitimacy to operate within their socially contracted regimes, it will be prudent to leverage on the robust and generally acceptable corporate reporting practices of conventional accounting. However, the findings suggest the need for a multidisciplinary approach to reporting corporate sustainability and value-added functions of the company.Following the emerging and increasing interest in value-added and sustainability reporting, countries like South Africa have enhanced their corporate sustainability disclosures (CSDs) through the use of acceptable value-added statements (VAS) and related metrics in their annual reports. Listed companies on the JSE Ltd have either produced a VAS, Sustainable Development Report (SDRs) or related CSDs by leveraging on existing reporting frameworks to meet the information user needs of the wider stakeholders. This thesis used a mixed method approach to examine the reasonable acceptability of the VAS as an ideal value added report by corporate organisations to meet the information user needs of the wider stakeholder groups. Additionally, this thesis sought to understand the detailed Sustainability and Value – Added Reporting (VAR) practices of corporate organisations by using the South African context as a case study. The quantitative approach revealed that there is a growing trend in the amount and volume of value-added and sustainability reports produced by listed firms in South Africa. It further revealed the increasing appetite by corporate entities to include infographics and supporting narratives to explain the sustainability and value added practices of the companies with the aim of gaining and maintaining legitimacy in their business environments. The qualitative findings suggest that value-added and sustainability reporting converge with and diverge from each other which requires a clearer delineation of these practices. Furthermore, the qualitative findings suggest that harmonizing the various sustainability reporting standards into common canons could take a while due to the consistently changing dynamics of sustainable development programmes. However, there is the need to effectively assure (audit) these value-added and sustainability programmes of corporate entities and possibly align them to generally acceptable reporting frameworks such as the UN System of National Accounting in order to unearth more items of values. In doing so, corporate value-added practices and sustainability programmes will go a long way to help the wider stakeholders make informed and useful decisions. The research concluded that in order for corporate entities in emerging economies like South Africa to gain the legitimacy to operate within their socially contracted regimes, it will be prudent to leverage on the robust and generally acceptable corporate reporting practices of conventional accounting. However, the findings suggest the need for a multidisciplinary approach to reporting corporate sustainability and value-added functions of the company

Integrated formal modeling and automated analysis of computer network attacks

Die vorhandenen Ansätze zur formalen Modellierung und Analyse von Computernetzwerksicherheit sind entweder auf eine Protokoll-, Knoten-, oder Netzwerksicht ausgerichtet. Meist beschränken sie sich sogar auf einen speziellen Teilbereich einer dieser Sichten (z.B. eine bestimmte Art von Protokollen, die Interaktion zwischen den lokalen Komponenten eines Knotens, oder die Ausbreitung vordefininierter Verletzlichkeiten). Insgesamt wird von jedem Ansatz jeweils nur ein kleiner Teil der Aspekte, die in praktischen Computernetzwerkangriffsszenarien vorkommen, abgedeckt. Hinzu kommen oft weitere Einschränkungen in Bezug auf Unterstützung dynamischer Änderungen, modellier- und untersuchbare Eigenschaften, benötigte Unterstützung der Analyse durch den Benutzer, usw. Um eine vollständigere Sicht auf Computernetzwerkangriffsszenarien zu erhalten, müssen daher mehrere Ansätze, und damit auch Modelle, Formalismen und Werkzeuge, eingesetzt werden. Sowohl die Modellierungs- als auch die Analysearbeit fallen damit mehrfach an und Konsistenz zwischen den verschiedenen Modellen und Analyseergebnissen lässt sich nur sehr schwer erreichen. In dieser Arbeit wird ein neuartiger Ansatz vorgestellt, der die Protokoll-, Knoten und Netzwerksicht auf mittlerer Detailebene übergreifend integriert. Die Modelle sind ausdrucksstark genug, um dynamische Änderungen zu beinhalten. Vielfältige Eigenschaften können über unterschiedliche Mechanismen spezifiziert werden. Da integrierte Modelle deutlich komplexer als eingeschränkte Modelle für einen Teilbereich sind, ist die Analyse besonders schwierig. Im Allgemeinen schlagen Ansätze zur automatischen Analyse schnell durch Zustandsraumexplosion fehl. Durch eine intelligente Modellierung, die Berücksichtigung von Optimierungsmöglichkeiten auf allen Ebenen, die Modellierung mit einer objektorientieren und kompositionalen, aber trotzdem auf einer einfachen Struktur basierenden Sprache, und dem Einsatz eines dem aktuellen Stand der Forschung entsprechenden Analysewerkzeuges sind wir trotzdem in der Lage, erfolgreich automatisiert zu analysieren. Unser Ansatz basiert auf der Spezifikationshochsprache CTLA 2003, einem Framework zur Modellierung von Computernetzwerkangriffsszenarien, einem Übersetzungsschema von CTLA 2003 nach PROMELA, dem CTLA2PC Übersetzungs- und Optimierungswerkzeug, und dem mächtigen Modellchecker SPIN. Die Durchführbarkeit unseres Ansatzes wird durch die Modellierung und Analyse von drei dynamischen Netzwerkszenarien zunehmender Komplexität aufgezeigt. In diesen Szenarien werden konkrete Angriffsfolgen als Verletzungen vorgegebener Sicherheitseigenschaften automatisch aufgedeckt.In the field of formal modeling and analysis as related to computer network security, existing approaches are highly specialized towards either a protocol, node, or network view. Typically, they are even further specialized towards a specific subset of one view (e.g., a certain class of protocols, interactions of local node components, or network propagation of predefined vulnerabilities). Thus, each approach covers only a small part of the aspects related to practical computer network attack scenarios. Often, further restrictions with respect to the dynamics allowed for the model, properties supported or user guidance required during analysis, have to be observed. Multiple approaches, and thus models, formalisms, and analysis tools, need to be employed to provide a more complete view of computer network attack scenarios. Both the modeling task and the analysis task have to be done multiple times and it is hard to ensure the consistency of the models and analysis results. We present a novel approach that comprehensively integrates the protocol, node, and network view on a middle level of detail. Furthermore, the models are expressive enough to support dynamic changes. A wide range of properties can be specified using different mechanisms. As integrated models naturally are of higher complexity than more specialized models limited to a single view, analysis is particularly challenging. Generally, automated analysis approaches quickly fail due to state space explosion effects. Nevertheless, by careful modeling, considering optimization possibilities at all stages, modeling using an object-oriented and compositional yet simple structured language, and employing a state of the art analysis tool we are able to achieve automated analysis. Our approach is based on the high-level specification language CTLA 2003, a framework for modeling computer network attack scenarios, a scheme for translating CTLA 2003 to PROMELA, the CTLA2PC translation and optimization tool, and the powerful model checker SPIN. For demonstrating the feasibility of our approach, the modeling and analysis of three case studies involving multi-node dynamic network scenarios is presented. In these case studies, precise attack sequences are automatically predicted as violations of abstract security properties

Essays on cultural and institutional dynamics in economic development using spatial analysis

This thesis seeks to research patterns of economic growth and development from a number of perspectives often resonated in the growth literature. By addressing themes about history, geography, institutions and culture the thesis is able to bring to bear a wide range of inter-related literatures and methodologies within a single content. Additionally, by targeting different administrative levels in its research design and approach, this thesis is also able to provide a comprehensive treatment of the economic growth dilemma from both cross-national and sub-national perspectives. The three chapters herein discuss economic development from two broad dimensions. The first of these chapters takes on the economic growth inquiry by attempting to incorporate cultural geography within a cross-country formal spatial econometric growth framework. By introducing the global cultural dynamics of languages and ethnic groups as spatial network mechanisms, this chapter is able to distinguish economic growth effects accruing from own-country productive efforts from those accruing from interconnections within a global productive network chain. From this, discussions and deductions about the implications for both developed and developing countries are made as regards potentials for gains and losses from such types and levels of productive integration. The second and third chapters take a different spin to the economic development inquiry. They both focus on economic activity in Africa, tackling the relevant issues from a geo-intersected dimension involving historic regional tribal homelands and modern national and subnational administrative territories. The second chapter specifically focuses on attempting to adopt historical channels to investigate the connection between national institutional quality and economic development in demarcated tribal homelands at the fringes of national African borders. The third chapter on the other hand focuses on looking closer at the effects of demarcations on economic activity. It particularly probes how different kinds of demarcation warranted by two different but very relevant classes of politico-economic players have affected economic activity quite distinguishably within the resulting subnational regions in Africa