Submitted by Daniella Sodre (daniella.sodre@ufpe.br) on 2015-04-17T14:15:28Z No. of bitstreams: 2 TESE Jucimar Maia da Silva Júnior.pdf: 4954306 bytes, checksum: fbddc0017ae748afd4a4afa5751c4a17 (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) / Made available in DSpace on 2015-04-17T14:15:28Z (GMT). No. of bitstreams: 2 TESE Jucimar Maia da Silva Júnior.pdf: 4954306 bytes, checksum: fbddc0017ae748afd4a4afa5751c4a17 (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Previous issue date: 2013-07-31 / Jogos via Internet, redes sociais e as novas aplicações web demandam acesso simultâneo e interativo de milhares (às vezes milhões) de pessoas. Esses sistemas são quase sempre desenvolvidos usando linguagens de script como PHP ou usando frameworks baseados em linguagens como Java, Ruby ou Pyhton. À proporção que o acesso a esses sistemas cresce, os fornecedores de tais serviços necessitam atender a novas demandas por meio da substituição de hardware por modelos mais potentes, aumentando seus custos operacionais. Quando o nível de acesso cresce drasticamente, o projetista se vê forçado a reprojetar toda a arquitetura do sistema migrando para soluções complexas usando Java Enterprise Edition (JEE) ou Node.js. Essas soluções também demandam mais e mais servidores. O problema possui uma raiz mais profunda: as linguagens de programação usadas para o desenvolvimento de sistemas não foram projetadas para suportar concorrência massiva. Linguagens com suporte a concorrência baseadas no modelo de memória compartilhada não possuem a escalabilidade necessária para atender a demanda. Para resolver os problemas ocasionados pela concorrência massiva, os desenvolvedores estão optando por usar linguagens funcionais como Scala e Erlang na arquitetura do sistema ao contrário de linguagens orientadas a objetos como Java. Mas Erlang não possui uma sintaxe própria para programação orientada a objetos. Este trabalho mostra o desenvolvimento de uma extensão orientada a objetos para a linguagem Erlang, chamada ooErlang, que possui uma melhor expressividade para resolução de problemas “do mundo real” e que não degrade o bom desempenho da linguagem em aplicações que demandam alto tráfego de dados e fina granularidade computacional, tal qual em programas Web 2.0. Assim sendo, o nicho da extensão aqui apresentada é o mesmo de Erlang: desenvolver sistemas backend para grandes aplicações onde a concorrência massiva e tolerância a falhas são requeridas.

Testing is the dominant technique for quality assurance of software systems. It typically consumes considerable resources in development projects, and is often performed in an ad hoc manner. This thesis is concerned with model-based testing, which is an approach to make testing more systematic and more automated. The general idea in model-based testing is to start from a formal model, which captures the intended behavior of the software system to be tested. On the basis of this model, test cases can be generated in a systematic way. Since the model is formal, the generation of test suites can be automated and with adequate tool support one can automatically quantify to which degree they exercise the tested software. Despite the significant improvements on model-based testing in the last 20 years, acceptance by industry has so far been limited. A number of commercially available tools exist, but still most testing in industry relies on manually constructed test cases. This thesis address this problem by presenting a methodology and associated tool support, which is intended to be used for model-based testing of communication protocol implementations in industry. A major goal was to make the developed tool suitable for industrial usage, implying that we had to consider several problems that typically are not addressed by the literature on model-based testing. The thesis presents several technical contributions to the area of model-based testing, including - a new specification language based on the functional programming language Erlang, - a novel technique for specifying coverage criteria for test suite generation, and - a technique for automatically generating test suites. Based on these developments, we have implemented a complete tool chain that generates and executes complete test suites, given a model in our specification language. The thesis also presents a substantial industrial case study, where our technical contributions and the implemented tool chain are evaluated. Findings from the case study include that test suites generated using (model) coverage criteria have at least as good fault-detection capability as equally large random test suites, and that model-based testing could discover faults in previously well-tested software where previous testing had employed a relaxed validation of requirements.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Eniro 118 118 AB is Sweden's largest enlightenment company. The company provides numerous operator-based services in addition to their main service 118 118. For a service company like Eniro 118 118 AB, the telephone operators required to provide its services represents a significant proportion of the total expenses. It is therefore of great interest for the company to maintain these costs at lowest possible levels. The current business cycle along with competition from new companies and new technological possibilities for its customers has led to a situation where the importance of an efficient resource planning is becoming increasingly more significant. The dilemma lies in the complexity and versatility of the operating system. A large number of telephone operators with a unique set of core skills are working simultaneously in three different systems that interact with each other according to certain predetermined rules. To determine the number of telephone operators required at any given time for each service is very complicated.The purpose of this thesis is to provide the planning office in Sundsvall with a tool that facilitates the resource planning activities on a daily basis. This is to be done by constructing a simulation model that looks and behaves like the real system, combined with an easy-to-use user interface that allow planners to test various staffing scenarios in a safe environment.The first step was to accurately create an understanding of, and to record exactly how Eniro 118 118 AB´s telephone system is structured. A number of interviews were conducted with the supervisor at Eniro 118 118 AB, who also provided certain documentation and lots of statistics. Additional interviews with stakeholders in the planning office were made in order to clarify how the user interface was to be designed, what parameters to make adjustable, and the types of results to be presented. The simulation model has been developed in the Simul8 simulation package as requested by Eniro 118 118 AB. The model has been designed to handle all requirements defined by the company and offers a complete tool for testing different staffing scenarios in a safe environment that behaves just like the real system. The user of the simulation model specifies input data such as operator availability, phone call arrival rate, average operation time and setup time for each service. After being run, the model will present the following results; operator workload, level of service and average wait time. The simulation model communicates and is controlled by MS Excel, which means that users do not need to learn Simul8 in order to use the product. Considering Eniro 118 118 AB’s requirements for documentation, a manual has been prepared which in detail describes how the simulation has been constructed and how Simul8 operates. This is to facilitate a possible future scenario in which current conditions no longer apply and the simulation model needs to be modified. / Validerat; 20111011 (anonymous)

ERLANG is a concurrent functional language, well suited for distributed, highly concurrent and fault-tolerant software. An important part of Erlang is its support for failure recovery. Fault tolerance is provided by organising the processes of an ERLANG application into tree structures. In these structures, parent processes monitor failures of their children and are responsible for their restart. Libraries support the creation of such structures during system initialisation.A technique to automatically analyse that the process structure of an ERLANG application from the source code is presented. The analysis exposes shortcomings in the fault tolerance properties of the application. First, the process structure is extracted through static analysis of the initialisation code of the application. Thereafter, analysis of the process structure checks two important properties of the fault handling mechanism: 1) that it will recover from any process failure, 2) that it will not hide persistent errors.The technique has been implemented in a tool, and applied it to several OTP library applications and to a subsystem of a commercial system the AXD 301 ATM switch.The static analysis of the ERLANG source code is achieved through symbolic evaluation. The evaluation is peformed according to an abstraction of ERLANG’s actual semamtics. The actual semantics is formalised for a nontrivial part of the language and it is proven that the abstraction of the semantics simulates the actual semantics. / ASTEC

This thesis investigates using an approach based on the Actors paradigm for implementing a discrete event simulation system and comparing the results with more traditional approaches. The goal of this work is to determine if using Actors for sequential programming is viable. If Actors are viable for this type of programming, then it follows that they would be usable for general programming. One potential advantage of using Actors instead of traditional paradigms for general programming would be the elimination of a distinction between designing for a sequential environment and a concurrent/distributed one. Using Actors for general programming may also allow for a single implementation that can be deployed on both single core and multiple core systems. Most of the existing discussions about the Actors model focus on its strengths in distributed environments and its ability to scale with the amount of available computing resources. The chosen system for implementation is intentionally sequential to allow for examination of the behaviour of existing Actors implementations where managing concurrency complexity is not the primary task. Multiple implementations of the simulation system were built using different languages (C++, Erlang, and Java) and different paradigms, including traditional ones and Actors. These different implementations were compared quantitatively, based on their execution time, memory usage, and code complexity. The analysis of these comparisons indicates that for certain existing development environments, Erlang/OTP, following the Actors paradigm, produces a comparable or better implementation than traditional paradigms. Further research is suggested to solidify the validity of the results presented in this research and to extend their applicability.

Trådning är svårt att få så effektivt som möjligt och det är komplicerat att skriva kod för det. Det här examensarbetet beskriver en implementation och jämför sedan implementationerna. Utvärderingen av implementationerna i Java, Jetlang och Erlang avslöjar att Jetlang skalar bäst både när det gäller komplexitet och hårdvara. Erlang behöver minst extra kod för att hantera trådning. När det gäller många små körningar har även Erlang bäst prestanda men tappar försprånget snabbt när komplexiteten ökar. / Efficient threading is difficult to create and it is complicated to write. This thesis describes an implementation and compares these. The evaluationof the implementations in Java, Jetlang and Erlang reveal that Jetlang is the best when it comes to scaling regarding complexity as well as hardware. Erlang requires the least extra code for the threading. When many small executions are needed, Erlang performs the best but loses the lead quickly when the complexity increases.

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.

Thousands of call centers operate in the United States employing millions of people. Since personnel costs represent as much as 80% of the total operating expense of these centers, it is important for call center managers to determine an appropriate staffing level required to maintain the desired operating performance. Historically, queueing models serve an important role in this regard. The one most commonly used is the Erlang-C model. The Erlang-C model has several assumptions, however, which are required for the predicted performance measures to be valid. One assumption that has received significant attention from researchers is that callers have infinite patience and will not terminate a call until the service is complete regardless of the wait time. Since this assumption is not likely to occur in reality, researchers have suggested using Erlang-A instead. Erlang-A does consider caller patience and allows for calls to be abandoned prior to receiving service. However, the use of Erlang-A still requires an assumption that is very unlikely to occur in practice - the assumption that all agents provide service at the same rate. Discrete event simulation is used to examine the effects of agent heterogeneity on the operating performance of a call center compared to the theoretical performance measures obtained from Erlang-A. Based on the simulation results, it is concluded that variability in agent service rate does not materially affect call center performance except to the extent that the variability changes the average handle time of the call center weighted by the number of calls handled and not weighted by agent. This is true regardless of call center size, the degree of agent heterogeneity, and the distribution shape of agent variability. The implication for researchers is that it is unnecessary to search for an analytic solution to relax the Erlang-A assumption that agents provide service at the same rate. Several implications for managers are discussed including the reliability of using Erlang-A to determine staffing levels, the importance of considering the service rates of the agents rather than the average handle time, and the unintended consequence of call routing schemes which route calls to faster rather than slower agents.

Compartmentalization is a general principle in biological systems which is observable on all size scales, ranging from organelles inside of cells, cells in histology, and up to the level of groups, herds, swarms, meta-populations, and populations. Compartmental models are often used to model such phenomena, but such models can be both highly nonlinear and difficult to work with. Fortunately, there are many significant biological systems that are amenable to linear compartmental models which are often more mathematically accessible. Moreover, the biology and mathematics is often so intertwined in such models that one can be used to better understand the other. Indeed, as we demonstrate in this paper, linear compartmental models of migratory dynamics can be used as an exciting and interactive means of introducing sophisticated mathematics, and conversely, the associated mathematics can be used to demonstrate important biological properties not only of seasonal migrations but also of compartmental models in general. We have found this approach to be of great value in introducing derivatives, integrals, and the fundamental theorem of calculus. Additionally, these models are appropriate as applications in a differential equations course, and they can also be used to illustrate important ideas in probability and statistics, such as the Poisson distribution.