Aplicações de sistemas computacionais emergentes atribuindo requisitos de resposta na forma de tempo de resposta requerem uma abordagem de sistemas de tempo real. Nesses sistemas, a qualidade de serviço é expressa como garantia das restrições temporais. Um amplo leque de técnicas para provisão de QoS encontram-se na literatura. Estas técnicas são baseadas tanto na diferenciação de serviço (QoS relativa), quanto na especificação de garantia de desempenho (QoS absoluta). Porém, a integração de QoS relativa e absoluta em nível de aplicação não tem sido tão explorada. Este trabalho realiza o estudo, a análise e a proposta de um método de escalonamento de tempo real em um ambiente simulado, baseado em contratos virtuais adaptativos e modelo re-alimentado. O objetivo é relaxar as restrições temporais dos usuários menos exigentes e priorizar usuários mais exigentes, sem degradar a qualidade do sistema como um todo. Para tanto, estratégias são exploradas em nível de escalonamento para o cumprimento dos contratos especificados por requisitos de tempo médio de resposta. Os resultados alcançados com o emprego do método proposto sinalizam uma melhoria em termos de qualidade de serviço relativa e absoluta e uma melhor satisfação dos usuários. Este trabalho também propõe uma extensão para os modelos convencionalmente estudados nesse contexto, ampliando a formulação original de duas classes para n classes de serviços / Emerging computer system application posing responsiveness requirement in the form of response time demand a real-time system approach. In these systems, the quality of service is expressed as guarantees on time constraints. A wide range of techniques for QoS provision is found in the literature. These techniques are based both on either service differentiation (relative QoS) or specification of performance guaranteeS (absolute QoS). However, integrated provision of both relative and absolute QoS at application level is not as well explored. This work conducts the study, analysis and proposal of a real time scheduling method in a simulated environment. This method is based on adaptive virtual contracts and feedback model. The goal is to relax the time constraints of less demanding users and prioritize the time constraints of most demanding users, without degrading the quality of the system as a whole. Strategies toward this goal are exploited in the system scheduling level and are aimed at the problem of fulfulling service-level agreements specifying average response times requirements. The results achieved with the proposed method indicate an improvement in relative and absolute QoS and a better user satisfaction. This work also proposes an extension to the conventional models studied in this context, extending the original formulation of two classes for n classes of services

Aplicações de sistemas computacionais emergentes atribuindo requisitos de resposta na forma de tempo de resposta requerem uma abordagem de sistemas de tempo real. Nesses sistemas, a qualidade de serviço é expressa como garantia das restrições temporais. Um amplo leque de técnicas para provisão de QoS encontram-se na literatura. Estas técnicas são baseadas tanto na diferenciação de serviço (QoS relativa), quanto na especificação de garantia de desempenho (QoS absoluta). Porém, a integração de QoS relativa e absoluta em nível de aplicação não tem sido tão explorada. Este trabalho realiza o estudo, a análise e a proposta de um método de escalonamento de tempo real em um ambiente simulado, baseado em contratos virtuais adaptativos e modelo re-alimentado. O objetivo é relaxar as restrições temporais dos usuários menos exigentes e priorizar usuários mais exigentes, sem degradar a qualidade do sistema como um todo. Para tanto, estratégias são exploradas em nível de escalonamento para o cumprimento dos contratos especificados por requisitos de tempo médio de resposta. Os resultados alcançados com o emprego do método proposto sinalizam uma melhoria em termos de qualidade de serviço relativa e absoluta e uma melhor satisfação dos usuários. Este trabalho também propõe uma extensão para os modelos convencionalmente estudados nesse contexto, ampliando a formulação original de duas classes para n classes de serviços / Emerging computer system application posing responsiveness requirement in the form of response time demand a real-time system approach. In these systems, the quality of service is expressed as guarantees on time constraints. A wide range of techniques for QoS provision is found in the literature. These techniques are based both on either service differentiation (relative QoS) or specification of performance guaranteeS (absolute QoS). However, integrated provision of both relative and absolute QoS at application level is not as well explored. This work conducts the study, analysis and proposal of a real time scheduling method in a simulated environment. This method is based on adaptive virtual contracts and feedback model. The goal is to relax the time constraints of less demanding users and prioritize the time constraints of most demanding users, without degrading the quality of the system as a whole. Strategies toward this goal are exploited in the system scheduling level and are aimed at the problem of fulfulling service-level agreements specifying average response times requirements. The results achieved with the proposed method indicate an improvement in relative and absolute QoS and a better user satisfaction. This work also proposes an extension to the conventional models studied in this context, extending the original formulation of two classes for n classes of services

The central thesis of this dissertation is that by combining classical scheduling methodologies with those of inventory management and queueing theory we can better model, understand and solve complex real-world scheduling problems. In part II of this dissertation, we provide models of a realistic supply chain scheduling problem that capture both its combinatorial nature and its dependence on inventory availability. We present an extensive empirical evaluation of how well implementations of these models in commercially available software solve the problem. We are therefore able to address, within a specific problem, the need for scheduling to take into account related decision-making processes. In order to simultaneously deal with combinatorial and dynamic properties of real scheduling problems, in part III we propose to integrate queueing theory and deterministic scheduling. Firstly, by reviewing the queueing theory literature that deals with dynamic resource allocation and sequencing and outlining numerous future work directions, we build a strong foundation for the investigation of the integration of queueing theory and scheduling. Subsequently, we demonstrate that integration can take place on three levels: conceptual, theoretical and algorithmic. At the conceptual level, we combine concepts, ideas and problem settings from the two areas, showing that such combinations provide insights into the trade-off between long-run and short-run objectives. Next, we show that theoretical integration of queueing and scheduling can lead to long-run performance guarantees for scheduling algorithms that have previously been proved only for queueing policies. In particular, we are the first to prove, in two flow shop environments, the stability of a scheduling method that is based on the traditional scheduling literature and utilizes processing time information to make sequencing decisions. Finally, to address the algorithmic level of integration, we present, in an extensive future work chapter, one general approach for creating hybrid queueing/scheduling algorithms. To our knowledge, this dissertation is the first work that builds a framework for integrating queueing theory and scheduling. Motivated by characteristics of real problems, this dissertation takes a step toward extending scheduling research beyond traditional assumptions and addressing more realistic scheduling problems.

The central thesis of this dissertation is that by combining classical scheduling methodologies with those of inventory management and queueing theory we can better model, understand and solve complex real-world scheduling problems. In part II of this dissertation, we provide models of a realistic supply chain scheduling problem that capture both its combinatorial nature and its dependence on inventory availability. We present an extensive empirical evaluation of how well implementations of these models in commercially available software solve the problem. We are therefore able to address, within a specific problem, the need for scheduling to take into account related decision-making processes. In order to simultaneously deal with combinatorial and dynamic properties of real scheduling problems, in part III we propose to integrate queueing theory and deterministic scheduling. Firstly, by reviewing the queueing theory literature that deals with dynamic resource allocation and sequencing and outlining numerous future work directions, we build a strong foundation for the investigation of the integration of queueing theory and scheduling. Subsequently, we demonstrate that integration can take place on three levels: conceptual, theoretical and algorithmic. At the conceptual level, we combine concepts, ideas and problem settings from the two areas, showing that such combinations provide insights into the trade-off between long-run and short-run objectives. Next, we show that theoretical integration of queueing and scheduling can lead to long-run performance guarantees for scheduling algorithms that have previously been proved only for queueing policies. In particular, we are the first to prove, in two flow shop environments, the stability of a scheduling method that is based on the traditional scheduling literature and utilizes processing time information to make sequencing decisions. Finally, to address the algorithmic level of integration, we present, in an extensive future work chapter, one general approach for creating hybrid queueing/scheduling algorithms. To our knowledge, this dissertation is the first work that builds a framework for integrating queueing theory and scheduling. Motivated by characteristics of real problems, this dissertation takes a step toward extending scheduling research beyond traditional assumptions and addressing more realistic scheduling problems.