Studies related to the process of program development

The submitted work consists of a collection of publications arising from research carried out at Rhodes University (1970-1980) and at Heriot-Watt University (1980-1992). The theme of this research is the process of program development, i.e. the process of creating a computer program to solve some particular problem. The papers presented cover a number of different topics which relate to this process, viz. (a) Programming methodology programming. (b) Properties of programming languages. aspects of structured. (c) Formal specification of programming languages. (d) Compiler techniques. (e) Declarative programming languages. (f) Program development aids. (g) Automatic program generation. (h) Databases. (i) Algorithms and applications

Index compression for information retrielval systems

[Abstract] Given the increasing amount of information that is available today, there is a clear need for Information Retrieval (IR) systems that can process this information in an efficient and effective way. Efficient processing means minimising the amount of time and space required to process data, whereas effective processing means identifying accurately which information is relevant to the user and which is not. Traditionally, efficiency and effectiveness are at opposite ends (what is beneficial to efficiency is usually harmful to effectiveness, and vice versa), so the challenge of IR systems is to find a compromise between efficient and effective data processing. This thesis investigates the efficiency of IR systems. It suggests several novel strategies that can render IR systems more efficient by reducing the index size of IR systems, referred to as index compression. The index is the data structure that stores the information handled in the retrieval process. Two different approaches are proposed for index compression, namely document reordering and static index pruning. Both of these approaches exploit document collection characteristics in order to reduce the size of indexes, either by reassigning the document identifiers in the collection in the index, or by selectively discarding information that is less relevant to the retrieval process by pruning the index. The index compression strategies proposed in this thesis can be grouped into two categories: (i) Strategies which extend state of the art in the field of efficiency methods in novel ways. (ii) Strategies which are derived from properties pertaining to the effectiveness of IR systems; these are novel strategies, because they are derived from effectiveness as opposed to efficiency principles, and also because they show that efficiency and effectiveness can be successfully combined for retrieval. The main contributions of this work are in indicating principled extensions of state of the art in index compression, and also in suggesting novel theoretically-driven index compression techniques which are derived from principles of IR effectiveness. All these techniques are evaluated extensively, in thorough experiments involving established datasets and baselines, which allow for a straight-forward comparison with state of the art. Moreover, the optimality of the proposed approaches is addressed from a theoretical perspective.[Resumen] Dada la creciente cantidad de información disponible hoy en día, existe una clara necesidad de sistemas de Recuperación de Información (RI) que sean capaces de procesar esa información de una manera efectiva y eficiente. En este contexto, eficiente significa cantidad de tiempo y espacio requeridos para procesar datos, mientras que efectivo significa identificar de una manera precisa qué información es relevante para el usuario y cual no lo es. Tradicionalmente, eficiencia y efectividad se encuentran en polos opuestos - lo que es beneficioso para la eficiencia, normalmente perjudica la efectividad y viceversa - así que un reto para los sistemas de RI es encontrar un compromiso adecuado entre el procesamiento efectivo y eficiente de los datos. Esta tesis investiga el problema de la eficiencia de los sistemas de RI. Sugiere diferentes estrategias novedosas que pueden permitir la reducción de los índices de los sistemas de RI, enmarcadas dentro da las técnicas conocidas como compresión de índices. El índice es la estructura de datos que almacena la información utilizada en el proceso de recuperación. Se presentan dos aproximaciones diferentes para la compresión de los índices, referidas como reordenación de documentos y pruneado estático del índice. Ambas aproximaciones explotan características de colecciones de documentos para reducir el tamaño final de los índices, mediante la reasignación de los identificadores de los documentos de la colección o bien descartando selectivamente la información que es "menos relevante" para el proceso de recuperación. Las estrategias de compresión propuestas en este tesis se pueden agrupar en dos categorías: (i) estrategias que extienden el estado del arte en la eficiencia de una manera novedosa y (ii) estrategias derivadas de propiedades relacionadas con los principios de la efectividad en los sistemas de RI; estas estrategias son novedosas porque son derivadas desde principios de la efectividad como contraposición a los de la eficiencia, e porque revelan como la eficiencia y la efectividad pueden ser combinadas de una manera efectiva para la recuperación de información. Las contribuciones de esta tesis abarcan la elaboración de técnicas del estado del arte en compresión de índices y también en la derivación de técnicas de compresión basadas en fundamentos teóricos derivados de los principios de la efectividad de los sistemas de RI. Todas estas técnicas han sido evaluadas extensamente con numerosos experimentos que involucran conjuntos de datos y técnicas de referencia bien establecidas en el campo, las cuales permiten una comparación directa con el estado del arte. Finalmente, la optimalidad de las aproximaciones presentadas es tratada desde una perspectiva teórica

The Third NASA Goddard Conference on Mass Storage Systems and Technologies

This report contains copies of nearly all of the technical papers and viewgraphs presented at the Goddard Conference on Mass Storage Systems and Technologies held in October 1993. The conference served as an informational exchange forum for topics primarily relating to the ingestion and management of massive amounts of data and the attendant problems involved. Discussion topics include the necessary use of computers in the solution of today's infinitely complex problems, the need for greatly increased storage densities in both optical and magnetic recording media, currently popular storage media and magnetic media storage risk factors, data archiving standards including a talk on the current status of the IEEE Storage Systems Reference Model (RM). Additional topics addressed System performance, data storage system concepts, communications technologies, data distribution systems, data compression, and error detection and correction

Structural Investigations on layered Manganites and Ruthenates

Die vorliegende Dissertation befasst sich mit der Präparation und der Strukturuntersuchung in zwei verschiedenen Übergangsmetalloxidfamilien. Zum Einen werden einfach-geschichtete Manganate betrachtet mit einem besonderen Fokus auf der Untersuchung der Ladungsordnung bei Halbdotierung. Hierzu wurden in einem ersten Schritt sowohl poly- als auch einkristalline Proben hergestellt wobei für letztere das Zonenschmelzverfahren zur Anwendung kam. Eine Untersuchung der ladungsgeordneten Phase der beiden Verbindungen La0.5Sr1.5MnO4 und Pr0.5Ca1.5MnO4 erfolgte mittels Röntgen- und Neutroneneinkristalldiffraktion. Die ladungsgeordnete Phase in La0.5Sr1.5MnO4 geht dabei aus einer hochsymmetrischen tetragonalen Phase mit der Raumgruppe I4/mmm hervor, in welcher die MnO6 Oktaeder keinerlei Verkippung oder Rotation aufweisen. Dieses stellt damit ein besonders einfach zu behandelndes Modellsystem dar. Das System Pr0.5Ca1.5MnO4 zeigt andererseits bereits eine Verkippung seiner MnO6 Oktaeder und ähnelt somit eher den stark verzerrten 3D Manganaten. Für beide Systeme konnte Struktur der ladungsgeordneten Phase bestimmt werden. Hierbei zeigte sich, dass das Zener-Polaron Modell die Struktur nicht beschreiben kann und stattdessen eine kombinierte Ladungs- und Orbitalordnung vorliegt. Weiterhin wurde für das System La0.5Sr1.5MnO4 die Substitution von Mangan durch Ruthenium untersucht. Hierbei wurden eine starke Schwächung der Ladungs- und Orbitalordnung und ein Absinken der Übergangstemperatur beobachtet. Obwohl schon ein Austausch von zehn Prozent Mangan die Ladungs- und Orbitalordnung unterdrücken kann konnte bis zu einer Dotierung von 30 Prozent kein metallisches Verhalten beobachtet werden. Ein weiterer Schwerpunkt dieser Arbeit liegt in der Untersuchung von geschichteten Ruthenaten. Hier konnte der Phasenverlauf des Metall-Isolator- und des strukturellen Übergangs in dem System Ca2-xSrxRuO4 präzise bestimmt werden. Die hierzu benötigten Proben bei hohen Kalziumkonzentrationen (x>0.2) wurden ebenfalls im Rahmen dieser Arbeit hergestellt. Weiterhin wurde in diesem System die Rotationsverzerrung untersucht, die bei hohen Strontiumkonzentrationen verschwindet. Mit diesen Daten konnte das Phasendiagram von O. Friedt und P. Steffens verfeinert werden. Für das System Ca3Ru2O7 wurde abschließend die Magnetstruktur in der paramagnetischen, der antiferromagnetisch metallischen und der antiferromagnetisch isolierenden Phase bestimmt

Logic and lattices for a statistics advisor

The work partially reported here concerned the development ot a prototype Expert System for giving advice about Statistics experiments, called ASA, and an inference engine to support ASA, called ABASE.This involved discovering what knowledge was necessary for performing the task at a satis¬ factory level of competence, working out how to represent this knowledge in a computer, and how to process the representations efficiently.Two areas of Statistical knowledge are described in detail: the classification of measure¬ ments and statistical variables, and the structure of elementary statistical experiments. A knowledge representation system based on lattices is proposed, and it is shown that such representations are learnable by computer programs, and lend themselves to particularly efficient implementation.ABASE was influenced by MBASE, the inference engine of MECHO [Bundy et al 79a]. Both are theorem provers working on typed function-free Horn clauses, with controlled creation of new entities. Their type systems and proof procedures are radically different, though, and ABASE is "conversational" while MBASE is not

Pattern Recognition

Pattern recognition is a very wide research field. It involves factors as diverse as sensors, feature extraction, pattern classification, decision fusion, applications and others. The signals processed are commonly one, two or three dimensional, the processing is done in real- time or takes hours and days, some systems look for one narrow object class, others search huge databases for entries with at least a small amount of similarity. No single person can claim expertise across the whole field, which develops rapidly, updates its paradigms and comprehends several philosophical approaches. This book reflects this diversity by presenting a selection of recent developments within the area of pattern recognition and related fields. It covers theoretical advances in classification and feature extraction as well as application-oriented works. Authors of these 25 works present and advocate recent achievements of their research related to the field of pattern recognition