Abstract
The ubiquity of data transformation problems in software engineering has led to the development of bidirectional transformation techniques in a variety of application domains. Model-driven engineering (MDE) is one of those areas, where such techniques are essential to maintain the consistency between multiple coexisting and simultaneously evolving models. However, the lack of in-depth research about certain characteristics of MDE has hindered the development of effective bidirectional model transformations that are able to address realistic MDE scenarios. This dissertation tackles two of these issues: that of constrained transformation domains and least-change transformations. The first regards the transformations’ ability to take into consideration the constraints imposed by the meta-models, and is essential to achieve correctness; the second regards the transformations’ ability to control the selection of updates from among those considered correct, and is essential to achieve a predictable system. These two issues are addressed under two popular bidirectional transformation schemes: in the context of the asymmetric framework of lenses, following a combinatorial approach; and in the context of the symmetric framework of constraint maintainers, proposing a solution based on model finding. The latter was effectively deployed as Echo, a tool for model repair and transformation. The expressiveness and flexibility provided by relational logic enabled it to be used as the unifying formalism throughout this dissertation.;A ubiquidade de problemas de transformação de dados em engenharia de software levou ao desenvolvimento de técnicas para transformação bidirecional numa variedade de domínios de aplicação. A Engenharia Baseada em Modelos (MDE) é uma dessas áreas, onde essas técnicas são essenciais para gerir a consistência entre múltiplos modelos que coexistem e evolvem simultaneamente. No entanto, a falta de estudos aprofundados sobre algumas características da MDE tem dificultado o desenvolvimento de técnicas de transformação bidirecional de modelos eficazes e que consigam lidar com cenários MDE realísticos. Esta dissertação aborda dois destes problemas: o de domínios de transformação restringidos e o de transformações com mudanças-mínimas. O primeiro tem que ver com a capacidade das transformações de ter em consideração as restrições impostas pelos meta-modelos e é essencial para atingir correcção; a segunda tem que ver com a capacidade de controlar a seleção de modificações entre as consideradas corretas, e é essencial para obter um sistema previsível. Esta tese aborda estes dois problemas sob dois populares esquemas de transformação bidirecional: no contexto da framework assimétrica das lentes, seguindo uma abordagem combinatorial, e no contexto da framework simétrica dos constraint maintainers, sendo proposta uma solução baseada em “procura de modelos”. Esta última foi efetivamente implementada como Echo, uma ferramenta para a reparação e transformação de modelos. A expressividade e flexibilidade proporcionada pela lógica relacional permitiu que esta fosse usada como o formalismo unificador desta dissertação.

Abstract
Traditional vertically integrated power utilities around the world have evolved from monopoly structures to open markets that promote competition among suppliers and provide consumers with a choice of services. Market forces drive the price of electricity and reduce the net cost through increased competition. Electricity can be traded in both organized markets or using forward bilateral contracts. This article focuses on bilateral contracts and describes some important features of an agent-based system for bilateral trading in competitive markets. Special attention is devoted to the negotiation process, demand response in bilateral contracting, and risk management. The article also presents a case study on forward bilateral contracting: a retailer agent and a customer agent negotiate a 24h-rate tariff.

Abstract
NoSQL databases opt not to offer important abstractions traditionally found in relational databases in order to achieve high levels of scalability and availability: transactional guarantees and strong data consistency. In this work we propose pH1, a generic middleware layer over NoSQL databases that offers transactional guarantees with Snapshot Isolation. This is achieved in a non-intrusive manner, requiring no modifications to servers and no native support for multiple versions. Instead, the transactional context is achieved by means of a multiversion distributed cache and an external transaction certifier, exposed by extending the client's interface with transaction bracketing primitives. We validate and evaluate pH1 with Apache Cassandra and Hyperdex. First, using the YCSB benchmark, we show that the cost of providing ACID guarantees to these NoSQL databases amounts to 11% decrease in throughput. Moreover, using the transaction intensive TPC-C workload, pH1 presented an impact of 22% decrease in throughput. This contrasts with OMID, a previous proposal that takes advantage of HBase's support for multiple versions, with a throughput penalty of 76% in the same conditions

Abstract
With the widespread deployment of wireless mesh networks (WMNs) in industrial environments, real-time (RT) communication may benefit from the multi-hop relaying infrastructure provided by WMNs. However, RT communication must be able to coexist with non-RT traffic sources that will interfere with RT communication. Within this context, this paper assesses the impact of interferences caused by non-RT traffic sources upon RT traffic in IEEE 802.11s mesh networks. Through an extensive set of simulations, we assess the impact of external traffic sources upon a set of RT message streams in different communication scenarios. According to the simulation results, we infer that RT traffic in 802.11s networks may be highly affected by external interferences, and therefore, such interferences must be taken into account when setting-up 802.11s networks. By varying the network load imposed by external interferences, we provide some useful hints about utilization thresholds above which the network can no longer reliably support RT traffic. We also present insights about the setting-up of some network parameters in order to optimize the RT communication performance.

Abstract
A bidirectional transformation consists of pairs of transformations-a forward transformation get produces a target view from a source, while a putback transformation put puts back modifications on the view to the source-satisfying sensible roundtrip properties. Existing bidirectional approaches are get-based in that one writes (an artifact resembling) a forward transformation and a corresponding backward transformation can be automatically derived. However, the unavoidable ambiguity that stems from the underspecification of put often leads to unpredictable bidirectional behavior, making it hard to solve nontrivial practical synchronization problems with existing bidirectional transformation approaches. Theoretically, this ambiguity problem could be solved by writing put directly and deriving get, but differently from programming with get it is easy to write invalid put functions. An open challenge is how to check whether the definition of a putback transformation is valid, while guaranteeing that the corresponding unique get exists. In this paper, we propose, as far as we are aware, the first safe language for supporting putback-based bidirectional programming. The key to our approach is a simple but powerful language for describing primitive putback transformations. We show that validity of putback transformations in this language is decidable and can be automatically checked. A particularly elegant and strong aspect of our design is that we can simply reuse and apply standard results for treeless functions and tree transducers in the specification of our checking algorithms. © 2014 Springer International Publishing Switzerland.

Abstract
Energy systems worldwide are complex and challenging environments. Multi-agent based simulation platforms are increasing at a high rate, as they show to be a good option to study many issues related to these systems, as well as the involved players at act in this domain. In this scope the authors’ research group has developed a multi-agent system: MASCEM (Multi- Agent System for Competitive Electricity Markets), which simulates the electricity markets environment. MASCEM is integrated with ALBidS (Adaptive Learning Strategic Bidding System) that works as a decision support system for market players. The ALBidS system allows MASCEM market negotiating players to take the best possible advantages from the market context. This paper presents the application of a Support Vector Machines (SVM) based approach to provide decision support to electricity market players. This strategy is tested and validated by being included in ALBidS and then compared with the application of an Artificial Neural Network, originating promising results. The proposed approach is tested and validated using real electricity markets data from MIBEL - Iberian market operator.