Thesis (MSc (Mathematical Sciences. Computer Science))--University of Stellenbosch, 2008. / Consider a path-oriented telecommunications network where calls arrive to each route in a Poisson process. Each call brings on average a fixed number of packets that are offered to route. The packet inter-arrival times and the packet lengths are exponentially distributed. Each route can queue a finite number of packets while one packet is being transmitted. Each accepted packet/call generates an amount of revenue for the route manager. At specified time instants a route manager can acquire additional capacity (“interface capacity”) in order to carry more calls and/or the manager can acquire additional buffer space in order to carry more packets, in which cases the manager earns more revenue; alternatively a route manager can earn additional revenue by selling surplus interface capacity and/or by selling surplus buffer space to other route managers that (possibly temporarily) value it more highly. We present a method for efficiently computing the buying and the selling prices of buffer space. Moreover, we propose a bandwidth reallocation scheme capable of improving the network overall rate of earning revenue at both the call level and the packet level. Our reallocation scheme combines the Erlang price [4] and our proposed buffer space price (M/M/1/K prices) to reallocate interface capacity and buffer space among routes. The proposed scheme uses local rules and decides whether or not to adjust the interface capacity and/or the buffer space. Simulation results show that the reallocation scheme achieves good performance when applied to a fictitious network of 30-nodes and 46-links based on the geography of Europe.

Thesis (MSc (Mathematical Sciences))--University of Stellenbosch, 2007. / The ever-increasing reliance of society on computer systems has led to a need for highly reliable systems. There are a number of areas where computer systems perform critical functions and the development of such systems requires a higher level of attention than any other type of system. The appropriate approach in this situation is known as formal methods. Formal methods refer to the use of mathematical techniques for the specification, development and verification of software and hardware systems. The two main goals of this thesis are: 1. The design of mathematical models as a basis for the implementation of error-free software for the safety interlock system at iThemba LABS (http://www.tlabs.ac.za/). 2. The comparison of formal method techniques that addresses the lack of much-needed empirical studies in the field of formal methods. Mathematical models are developed using model checkers: Spin, Uppaal, Smv and a theorem prover Pvs. The criteria used for the selection of the tools was based on the popularity of the tools, support of the tools, representation of properties, representativeness of verification techniques, and ease of use. The procedure for comparing these methods is divided into two phases. Phase one involves the time logging of activities followed by a novice modeler to model check and theorem prove software systems. The results show that it takes more time to learn and use a theorem prover than a model checker. Phase two involves the performance of the tools in relation to the time taken to verify a property, memory used, number of states and transitions generated. In spite of the differences between models, the results are in favor of Smv and this maybe attributed to the nature of the safety interlock system, as it involves a lot of hard-wired lines.

Thesis (Msc (Mathematical Sciences. Computer Science))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: Model checkers are programs that automatically verify, without human assistance, that certain user-specified properties hold in concurrent software systems. Since these programs often have expensive time and memory requirements, an active area of research is the development of distributed model checkers that run on clusters. Of particular interest is how the communication between the machines can be reduced to speed up their running time. In this thesis the design decisions involved in an on-the-fly distributed model checker are identified and discussed. Furthermore, the implementation of such a program is described. The central idea behind the algorithm is the generation and distribution of data throughout the nodes of the cluster. We introduce several techniques to reduce the communication among the nodes, and study their effectiveness by means of a set of models. / AFRIKAANSE OPSOMMING: Modeltoetsers is programme wat outomaties bevestig, sonder enige hulp van die gebruiker, dat gelopende sagteware aan sekere gespesifiseerde eienskappe voldoen. Die feit dat hierdie programme dikwels lang looptye en groot geheues benodig, het daartoe aanleiding gegee dat modeltoetsers wat verspreid oor ’n groep rekenaars hardloop, aktief nagevors word. Dit is veral belangrik om vas te stel hoe die kommunikasie tussen rekenaars verminder kan word om sodoende die looptyd te verkort. Hierdie tesis identifiseer en bespreek die ontwerpsbesluite betrokke in die ontwikkeling van ’n verspreide modeltoetser. Verder word die implementasie van so ’n program beskryf. Die kernidee is die generasie en verspreiding van data na al die rekenaars in die groep wat aan die probleem werk. Ons stel verskeie tegnieke voor om die kommunikasie tussen die rekenaar te verminder en bestudeer die effektiwiteit van hierdie tegnieke aan die hand van ’n lys modelle.

Thesis (MSc (Mathematical Sciences. Computer Science))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: Since 2002 data tra c has overtaken voice tra c in volume [1]. Telecom / Network operators still generate most of their income carrying voice tra c. There is however a huge revenue potential in delivering reliable guaranteed data services. Network survivability and recovery from network failures are integral to network reliability. Due to the nature of the Internet, recovery from link failures needs to be distributed and dynamic in order to be scalable. Link failure recovery schemes are evaluated in terms of the survivability of the network, the optimal use of network resources, scalability, and the recovery time of such schemes. The need for recovery time to be improved is highlighted by real-time data tra c such as VoIP and video services carried over the Internet. The goal of this thesis is to examine existing link failure recovery schemes and evaluate the need for their extension, and to evaluate the performance of the proposed link failure recovery schemes. i / AFRIKAANSE OPSOMMING: Sedert 2002 het data verkeer die stem verkeer in volume verbygesteek [1]. Telekommunikasie / netwerk operateurs genereer egter steeds die meeste van hul inkomste met stem verkeer. Netwerk oorlewing en die herstel van netwerk mislukkings is integraal tot netwerk stabiliteit. Die samestelling van die Internet noodsaak dat die herstel van skakel mislukkings verspreid en dinamies van natuur moet wees. Die herstel-skema van skakel mislukkings word evalueer in terme van die oorleefbaarheid van die netwerk, die mees e ektiewe benutting van network bronne, aanpasbaarheid, en die herstel tydperk van die skema. Die vinnig moontlikste herstel tydperk word genoodsaak deur oombliklike data verkeer soos VoIP en beeld dienste wat oor die Internet gedra word. The doel van hierdie tesis is om bestaande skakel mislukking herstel skemas te evalueer, en dan verder ondersoek in te stel na hul uitbreiding. Daarna word die voorgestelde skakel mislukking skema se e ektiwiteit gemeet.

Thesis (MSc (Computer Science))--University of Stellenbosch, 2005. / Sign Languages such as South African Sign Language, are proper natural languages; they have their own vocabularies, and they make use of their own grammar rules. However, machine translation from a spoken to a signed language creates interesting challenges. These problems are caused as a result of the differences in character between spoken and signed languages. Sign Languages are classified as visual-spatial languages: a signer makes use of the space around him, and gives visual clues from body language, facial expressions and sign movements to help him communicate. It is the absence of these elements in the written form of a spoken language that causes the contextual ambiguities during machine translation. The work described in this thesis is aimed at resolving the ambiguities caused by a translation from written English to South African Sign Language. We designed and implemented a preprocessor that uses areas of linguistics such as anaphora resolution and a data structure called a scene graph to help with the spatial aspect of the translation. The preprocessor also makes use of semantic and syntactic analysis, together with the help of a semantic relational database, to find emotional context from text. This analysis is then used to suggest body language, facial expressions and sign movement attributes, helping us to address the visual aspect of the translation. The results show that the system is flexible enough to be used with different types of text, and will overall improve the quality of a machine translation from English into a Sign Language.

Thesis (MSC (Mathematical Sciences. Computer Science))--Stellenbosch University, 2008. / This thesis describes the design and implementation of an application names GrailKnights that allows for the mass manipulation of automata, with added visual pattern analysis features. It comprises a database-driven backend for automata storage, and a graphical user interface that allows for filtering the automata selected from the database with visual interpretation of visible patterns over the resulting automata.

Thesis (MSc (Computer Science))-- University of Stellenbosch, 2001. / ENGLISH ABSTRACT: This thesis explores the use of neural networks for predicting difficult, real-world time series. We first establish and demonstrate methods for characterising, modelling and predicting well-known systems. The real-world system we explore is seismic event data obtained from a South African gold mine. We show that this data is chaotic. After preprocessing the raw data, we show that neural networks are able to predict seismic activity reasonably well. / AFRIKAANSE OPSOMMING: Hierdie tesis ondersoek die gebruik van neurale netwerke om komplekse, werklik bestaande tydreekse te voorspel. Ter aanvang noem en demonstreer ons metodes vir die karakterisering, modelering en voorspelling van bekende stelsels. Ons gaan dan voort en ondersoek seismiese gebeurlikheidsdata afkomstig van ’n Suid-Afrikaanse goudmyn. Ons wys dat die data chaoties van aard is. Nadat ons die rou data verwerk, wys ons dat neurale netwerke die tydreekse redelik goed kan voorspel. / Integrated Seismic Systems International

Thesis (MScIng)--University of Stellenbosch, 2006. / ENGLISH ABSTRACT: We designed a generic avatar animator for use in sign language related projects. The animator is capable of animating any given avatar that is compliant with the H-Anim standard for humanoid animation. The system was designed with the South African Sign Language Machine Translation (SASL-MT) project in mind, but can easily be adapted to other sign language projects due to its generic design. An avatar that is capable of accurately performing sign language gestures is a special kind of avatar and is referred to as a signing avatar. In this thesis we investigate the special characteristics of signing avatars and address the issue of finding a generic design for the animation of such an avatar. / AFRIKAANSE OPSOMMING: Ons het ’n generiese karakteranimasiestelsel ontwikkel vir gebruik in gebaretaal verwante projekte. Die animasiestelsel het die vermo¨e om enige karaktermodel wat met die H-Anim standaard versoenbaar is, te animeer. Die animasiestelsel is ontwerp met die oog op gebruik in die South African Sign Language Machine Translation (SASL-MT) projek, maar kan maklik aangepas word vir ander gebaretaalprojekte te danke aan die generiese ontwerp. ’n Karaktermodel wat in staat is om gebare akkuraat te maak is ’n spesiale tipe karaktermodel wat bekend staan as ’n gebaretaal avatar (Engels : signing avatar). In hierdie tesis ondersoek ons die spesiale eienskappe van ’n gebaretaal avatar en beskou die soektog na ’n generiese ontwerp vir die animering van so ’n karaktermodel.

Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: This thesis investigate the di erent available GSM bearer channels that can be used to launch a cellphone banking application. Speci c attention is given to launch such a cellphone banking application to the so called \bottom of the pyramid". In South Africa, there are an estimate 11 to 13 million people with no bank accounts. The cellphone create an ideal opportunity to be used as a tool to reach this untapped market segment that today mainly uses cash to pay for day to day living expenses. The thesis provide more information on the cellphone banking arena in South Africa as well as certain projects in other parts of the world. The thesis also highlight new devel- opments on cellphone technology that include Android and IPhone delivery channels. Focus is placed on how the cellphone banking presentation layer must be delivered through the USSD GSM bearer channel. USSD is at the current moment the ultimate channel to consider due to its extensive reach and ability to work on any GSM cellphone handset. In conclusion, although cellphone banking can be used by any person, the bene t to bring nancial services to the bottom end of the pyramid must be considered to achieve nancial inclusion. The cellphone due to its reach is the ideal medium to access this lower end market. / AFRIKAANSE OPSOMMING: Hierdie tesis ondersoek beskikbare GSM selfoon kanale wat gebruik kan word om 'n selfoon bankdienste toepassing te initieer. Spesi eke aandag word gegee om so 'n selfoon bankdienste toepassing uit te rol na die sogenaamde onderste gedeelte van die bevolkings piramiede. Die tesis verskaf meer informasie oor die selfoon bankdienste arena in Suid Africa maar dit brei ook ooit oor sekere soortgelyke projekte in ander dele van die wereld. Die tesis lig ook nuwe ontwikkelings uit in selfoon tegnologie wat Android en IPhone mediums insluit. Fokus word geplaas op die selfoon bankdienste vertoning deur die USSD GSM kanaal. USSD is huidiglik die beste kanaal om te oorweeg as gevolg van die wydverspreide beskik- baarheid omdat die tegnologie op enige selfoon handstuk werk. Die uiteindelike gevolgtrekking uit die werkstuk is dat selfoon bankdienste deur enige persoon gebruik kan word, maar selfoon bankdienste is 'n goeie idee om te oorweeg om mense in te sluit uit die onderste gedeelte van die bevolkings piramiede. Die selfoon kan dus as 'n ideale medium gebruik word om hierdie mense te betrek by nansiele dienste.

Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: We investigate the application of weighted tree transducers to correcting grammatical errors in natural language. Weighted finite-state transducers (FST) have been used successfully in a wide range of natural language processing (NLP) tasks, even though the expressiveness of the linguistic transformations they perform is limited. Recently, there has been an increase in the use of weighted tree transducers and related formalisms that can express syntax-based natural language transformations in a probabilistic setting. The NLP task that we investigate is the automatic correction of grammar errors made by English language learners. In contrast to spelling correction, which can be performed with a very high accuracy, the performance of grammar correction systems is still low for most error types. Commercial grammar correction systems mostly use rule-based methods. The most common approach in recent grammatical error correction research is to use statistical classifiers that make local decisions about the occurrence of specific error types. The approach that we investigate is related to a number of other approaches inspired by statistical machine translation (SMT) or based on language modelling. Corpora of language learner writing annotated with error corrections are used as training data. Our baseline model is a noisy-channel FST model consisting of an n-gram language model and a FST error model, which performs word insertion, deletion and replacement operations. The tree transducer model we use to perform error correction is a weighted top-down tree-to-string transducer, formulated to perform transformations between parse trees of correct sentences and incorrect sentences. Using an algorithm developed for syntax-based SMT, transducer rules are extracted from training data of which the correct version of sentences have been parsed. Rule weights are also estimated from the training data. Hypothesis sentences generated by the tree transducer are reranked using an n-gram language model. We perform experiments to evaluate the performance of different configurations of the proposed models. In our implementation an existing tree transducer toolkit is used. To make decoding time feasible sentences are split into clauses and heuristic pruning is performed during decoding. We consider different modelling choices in the construction of transducer rules. The evaluation of our models is based on precision and recall. Experiments are performed to correct various error types on two learner corpora. The results show that our system is competitive with existing approaches on several error types. / AFRIKAANSE OPSOMMING: Ons ondersoek die toepassing van geweegde boomoutomate om grammatikafoute in natuurlike taal outomaties reg te stel. Geweegde eindigetoestand outomate word suksesvol gebruik in ’n wye omvang van take in natuurlike taalverwerking, alhoewel die uitdrukkingskrag van die taalkundige transformasies wat hulle uitvoer beperk is. Daar is die afgelope tyd ’n toename in die gebruik van geweegde boomoutomate en verwante formalismes wat sintaktiese transformasies in natuurlike taal in ’n probabilistiese raamwerk voorstel. Die natuurlike taalverwerkingstoepassing wat ons ondersoek is die outomatiese regstelling van taalfoute wat gemaak word deur Engelse taalleerders. Terwyl speltoetsing in Engels met ’n baie hoë akkuraatheid gedoen kan word, is die prestasie van taalregstellingstelsels nog relatief swak vir meeste fouttipes. Kommersiële taalregstellingstelsels maak oorwegend gebruik van reël-gebaseerde metodes. Die algemeenste benadering in onlangse navorsing oor grammatikale foutkorreksie is om statistiese klassifiseerders wat plaaslike besluite oor die voorkoms van spesifieke fouttipes maak te gebruik. Die benadering wat ons ondersoek is verwant aan ’n aantal ander benaderings wat geïnspireer is deur statistiese masjienvertaling of op taalmodellering gebaseer is. Korpora van taalleerderskryfwerk wat met foutregstellings geannoteer is, word as afrigdata gebruik. Ons kontrolestelsel is ’n geraaskanaal eindigetoestand outomaatmodel wat bestaan uit ’n n-gram taalmodel en ’n foutmodel wat invoegings-, verwyderings- en vervangingsoperasies op woordvlak uitvoer. Die boomoutomaatmodel wat ons gebruik vir grammatikale foutkorreksie is ’n geweegde bo-na-onder boom-na-string omsetteroutomaat geformuleer om transformasies tussen sintaksbome van korrekte sinne en foutiewe sinne te maak. ’n Algoritme wat ontwikkel is vir sintaksgebaseerde statistiese masjienvertaling word gebruik om reëls te onttrek uit die afrigdata, waarvan sintaksontleding op die korrekte weergawe van die sinne gedoen is. Reëlgewigte word ook vanaf die afrigdata beraam. Hipotese-sinne gegenereer deur die boomoutomaat word herrangskik met behulp van ’n n-gram taalmodel. Ons voer eksperimente uit om die doeltreffendheid van verskillende opstellings van die voorgestelde modelle te evalueer. In ons implementering word ’n bestaande boomoutomaat sagtewarepakket gebruik. Om die dekoderingstyd te verminder word sinne in frases verdeel en die soekruimte heuristies besnoei. Ons oorweeg verskeie modelleringskeuses in die samestelling van outomaatreëls. Die evaluering van ons modelle word gebaseer op presisie en herroepvermoë. Eksperimente word uitgevoer om verskeie fouttipes reg te maak op twee leerderkorpora. Die resultate wys dat ons model kompeterend is met bestaande benaderings op verskeie fouttipes.