This dissertation develops a cost model for a particular implementation of the database query language GraphLog. The order in which the subgoals of a GraphLog query are executed has a major effect on the total processing time. Our model may be used to compare the expected execution costs for different orderings of the same general query, thus, allowing us to select an efficient execution plan. We describe two cost models: one that is tailored to a specific architecture and another that is more general. Both models assume a top-down evaluation strategy. In particular, we address the issue of how to handle recursive predicates. We also provide some experimental results that confirm the validity of our work. / Graduate

Java’s cross-platform virtual machine arrangement and its special features that make it ideal for writing network applications, also have a tremendous negative impact on its operations. In spite of its relatively weak performance, Java’s success has motivated the search for techniques to enhance its execution. This work presents the JAFARDD (a Java Architecture based on a Folding Algorithm, with Reservation stations, Dynamic translation, and Dual processing) processor designed to accelerate Java processing. JAFARDD dynamically translates Java bytecodes to RISC instructions to facilitate the use of a typical general-purpose RISC core. This enables the exploitation of the instruction level parallelism among the translated instructions using well established techniques, and facilitates the migration to Java-enabled hardware. Designing hardware for Java requires an extensive knowledge and understanding of its instruction set architecture which were acquired through a comprehensive behavioral analysis by benchmarking. Many aspects of the Java workload behavior were collected and the resulting statistics were analyzed. This helped identify performance-critical aspects that are candidates for hardware support. Our analysis surpasses other similar ones in terms of the number of aspects studied and the coverage of the recommendations made. Next, a global analysis of the design space of Java processors was carried out. Different hardware design options and alternatives that are suitable for Java were explored and their trade-offs were examined. We especially focused on the design methodology, execution engine organization, parallelism exploitation, and support for high-level language features. This analysis helped identify innovative design ideas such as the use of a modified Tomasulo’s algorithm. This, in turn, motivated the development of a bytecode folding algorithm that integrates with the reservation station concept in JAFARRD. While examining the behavioral analysis and the design space exploration ideas, a list of global architectural design principles started to emerge. These principles ensure JAFARRD can execute Java efficiently and are taken into consideration while the various instruction pipeline modules were designed. Results from the behavioral analysis also confirmed that Java’s stack architecture creates virtual data dependencies that limit performance and prohibit instruction level parallelism. To overcome this drawback, stack operation folding has been suggested in the literature to enhance performance by grouping contiguous instructions that have true data dependencies into a compound instruction. We have developed a folding algorithm that, unlike existing ones, does not require the folded instructions to be consecutive. To the best of our knowledge, our folding algorithm is the only one that permits nested pattern folding, tolerates variations in folding groups, and detects and resolves folding hazards completely. By incorporating this algorithm into a Java processor, the need for, and therefore the limitations of, a stack are eliminated. In addition to an efficient dual processing configuration (i.e., Java and RISC), JAFARDD is empowered with a number of innovative design features, including: an adaptive feedback fetch policy that copes with the variation in Java instruction size, a smart bytecode queue that compensates for the lack of a stack, an on-chip local variable file to facilitate operand access, an early tag assignment to dispatched instructions to reduce processing delay, and a specialized load/store unit that preprocesses object-oriented instructions. The functionality of JAFARDD has been successfully demonstrated through VHDL modeling and simulation. Furthermore, benchmarking using SPECjvm98 showed that the introduced techniques indeed speed up Java execution. Our bytecode folding algorithm speeds up execution by an average of about 1.29, eliminating an average of 97% of the stack instructions and 50% of the overall instructions. Compared to other proposals, JAFARDD combines Java bytecode folding with dynamic hardware translation, while maintaining the RISC nature of the processor, making this a much more flexible and general approach. / Graduate

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The simplest and most widely used queueing model in call centres is the M/M/k system, sometimes referred to as Erlang-C. For many applications the model is an over-simplification. Erlang-C model ignores among other things busy signals, customer impatience and services that span multiple visits. Although the Erlang-C formula is easily implemented, it is not easy to obtain insight from its answers (for example, to find an approximate answer to questions such as "how many additional agents do I need if the arrival rate doubles?"). An approximation of the Erlang-C formula that gives structural insight into this type of question would be of use to better understand economies of scale in call centre operations. Erlang-C based predictions can also turn out highly inaccurate because of violations of underlying assumptions and these violations are not straightforward to model. For example, non-exponential service times lead one to the M/G/k queue which, in stark contrast to the M/M/k system, is difficult to analyse. This thesis deals mainly with the general M/GI/k model with abandonment. The arrival process conforms to a Poisson process, service durations are independent and identically distributed with a general distribution, there are k servers, and independent and identically distributed customer abandoning times with a general distribution. This thesis will endeavour to analyse call centres using M/GI/k model with abandonment and the data to be used will be simulated using EZSIM-software. The paper by Brown et al. [3] entitled "Statistical Analysis of a Telephone Call Centre: A Queueing-Science Perspective," will be the basis upon which this thesis is built.

Occam is designed for concurrent programming on a network of transputers. AIlocation and partitioning of the program is specified within the source code, binding the program to a specific network. An altemative approach is proposed which completely separates the source code from hardware considerations. Static allocation is performed as a separate phase and should, ideally, be automatic but at present is manual. Complete hardware abstraction requires that non-local, shared communication be provided for, introducing an efficiency overhead which can be minimised by the allocation. The proposal was implemented on a network of IBM PCs, modelled on a transputer network, and implementation issues are discussed

Since the introduction of the IP Multimedia Subsystem (IMS) by the Third Generation Partnership Project (3GPP) in 2002, a lot of research has been conducted aimed at designing and implementing IMS capable clients and network elements. Though considerable work has been done in the development of IMS clients, there is no single, free and open source IMS client that provides researchers with all the required functionality needed to test the applications they are developing. For example, several open and closed source SIP/IMS clients are used within the Rhodes University Conver- gence Research Group (RUCRG) to test applications under development, as a result of the fact that the various SIP/IMS clients support different subsets of SIP/IMS features. The lack of a single client and the subsequent use of various clients comes with several problems. Researchers have to know how to deploy, configure, use and at times adapt the various clients to suit their needs. This can be very time consuming and, in fact, contradicts the IMS philosophy (the IMS was proposed to support rapid service creation). This thesis outlines the development of a Java-based, IMS compliant client called RUCRG IMS client, that uses the JAIN SIP Applet Phone (JSAP) as its foundation. JSAP, which originally offered only basic voice calling and instant messaging (IM) capabilities, was modified to be IMS compliant and support video calls, IM and presence using XML Configuration Access Protocol (XCAP).

Governments all over the world are faced with numerous challenges while running their countries on a daily basis. The predominant challenges which arise are those which involve statistical methodologies. Official statistics to South Africa’s infrastructure are very important and because of this it is important that an effort is made to reduce the challenges that occur during the development of official statistics. For official statistics to be developed successfully quality standards need to be built into an organisational framework and form a system of architecture (Statistics New Zealand 2009:1). Therefore, this study seeks to develop a statistical methodology that is appropriate and scientifically correct using an automated statistical system for audits in government regulatory authorities. The study makes use of Mathematica to provide guidelines on how to develop and use an automated statistical audit system. A comprehensive literature study was conducted using existing secondary sources. A quantitative research paradigm was adopted for this study, to empirically assess the demographic characteristics of tenants of Social Housing Estates and their perceptions towards the rental units they inhabit. More specifically a descriptive study was undertaken. Furthermore, a sample size was selected by means of convenience sampling for a case study on SHRA to assess the respondent’s biographical information. From this sample, a pilot study was conducted investigating the general perceptions of the respondents regarding the physical conditions and quality of their units. The technical development of an automated statistical audit system was discussed. This process involved the development and use of a questionnaire design tool, statistical analysis and reporting and how Mathematica software served as a platform for developing the system. The findings of this study provide insights on how government regulatory authorities can best utilise automated statistical audits for regulation purposes and achieved this by developing an automated statistical audit system for government regulatory authorities. It is hoped that the findings of this study will provide government regulatory authorities with practical suggestions or solutions regarding the generating of official statistics for regulatory purposes, and that the suggestions for future research will inspire future researchers to further investigate automated statistical audit systems, statistical analysis, automated questionnaire development, and government regulatory authorities individually.

Over the past few years, much experience has been gained in semi-automatic protocol implementation using an existing Estelle-C compiler developed at the University of British Columbia. However, with the continual evolution of the Estelle language, that compiler is now obsolete. The present study found substantial syntactic and semantic differences between the Estelle language as implemented by the existing compiler and that specified in the latest ISO document to warrant the construction of a new Estelle-C compiler. The result is a new compiler which translates Estelle as defined in the second version of the ISO Draft Proposal 9074 into the programming language C. The new Estelle-C compiler addresses issues such as dynamic reconfiguration of modules and maintenance of priority relationships among nested modules. A run-time environment capable of supporting the new Estelle features is also presented. The implementation strategy used in the new Estelle-C compiler is illustrated by using the alternating bit protocol found in the ISO Draft Proposal 9074 document. / Science, Faculty of / Computer Science, Department of / Graduate

Adhering to the principles of logic programming results in greater expressiveness than is obtained by using the many non-logical features which have been grafted onto current logic programming languages such as Prolog. This report describes an alternative approach to high performance logic programming in which the language and its implementation were designed together. Prolog's non-logical features are discarded and new logical ones are added. Extended pure Prolog (xpProlog) is a superset of conventional Prolog; it is sufficient in itself, without any need for "impure" non-logical predicates. This gives both greater expressiveness and better performance than conventional Prologs. XpProlog programs have the following advantages over conventional Prolog programs: • They are often easier to understand because their meaning does not rely on the underlying computational mechanism. • Coroutining, automatic delaying and sound negation are available. • As technology improves, better implementations and optimization techniques can be used without affecting existing programs. This report covers: • The proper use of logic programming. • How Prolog must be changed to become a good logic programming language (xpProlog). • Sound negation and coroutining. • An efficient abstract machine (xpPAM) which can be efficiently emulated on conventional machines, translated to conventional machine code, or implemented in special purpose hardware. • How to compile extended Prolog and functional (applicative) languages to the abstract machine or to conventional machine code. • Discussion of alternative Prolog abstract machine designs. The xpProlog Abstract Machine's design allows: • Performance similar to the Warren Abstract Machine (WAM) for sequential programs. • Tail recursion optimization (TRO). • Parallelism and coroutining with full backtracking. • Dynamic optimization of clause order. • Efficient if-then-else ("shallow" backtracking). • Simple, regular instruction set for easily optimized compilation. • Efficient memory utilization. • Integrated object-oriented virtual memory. • Predicates as first-class objects. • Simple extension to functional programming. C.R. categories: 1.2.5: Prolog; D.1.3: concurrent programming; D.3.2: very high level languages; D.3.3: language constructs: coroutines, backtracking; D.3.4: 1 interpreters.; 1.2.3: logic programming. / Science, Faculty of / Computer Science, Department of / Graduate