https://www.um.edu.mt/library/oar/handle/123456789/106750 Mon, 20 Apr 2026 04:05:54 GMT 2026-04-20T04:05:54Z https://www.um.edu.mt/library/oar/handle/123456789/135067 Title: Causal consistency through a novel distributed middleware over strongly consistent transaction processing Abstract: Our research deals with the concept of causal consistency of data in the context of transactional information systems with scalability and high availability require- ments. We deal with the consistency of data which is stored and replicated in multiple physical locations. Given the data store’s distributed nature, a new set of data inconsistency issues arise. These cause clients to get an inconsistent, and therefore possibly incorrect, view of the data, yielding application errors and even susceptibility to security vulnerabilities. Most problems do not impact centralised databases, but centralised databases do not provide the resiliency and performance characteristics required by modern enterprise transactional information systems. We focus on this set of data inconsistency problems, and propose solutions to strengthen consistency guarantees without jeopardising the benefits of a distributed database. We model causal consistency, the strongest type of consistency that can be implemented in fault-tolerant, scalable databases, using the Actor model of com- putation. The model is then implemented on top of commercially-ready relational database management systems that are built to provide strong consistency. Data Inconsistency, Transaction Inconsistency and Integrity Invariant Violation are three related, but distinct, problems tackled in this research. For each prob- lem, we review the literature as well as design, implement and evaluate a novel solution. Our work shows that it is possible to have a distributed middleware that implements causal consistency with transaction consistency and integrity invariant preservation over a set of disconnected relational databases deployed within geo- graphically distributed data centres. Thus, our approach addresses each problem whilst answering to the scalability and resiliency needs of modern systems. Empirical results show that our middleware achieves better performance when compared to a single-node (i.e., non-distributed) relational database management system. We also extend our solution for Data Inconsistency and deploy the middle- ware on many machines within a data centre. In doing so, we identify and propose solutions for the complexities that arise from scaling the middleware horizontally, whilst our benchmarks show a significant increase in the amount of operations that can be processed at each data centre, and that data changes are replicated across geographically distributed instances of the system within acceptable timeframes. Description: Ph.D.(Melit.) Sun, 01 Jan 2023 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/135067 2023-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/131928 Title: Miniature implementation of an IoT‐based smart city Abstract: Ever since the idea of a Smart City was introduced, the Internet of Things (IoT) has been a key pillar of the technological aspect of Smart City development. Cities should fully grasp the advantages and opportunities of the IoT for Smart Cities since there is so much promise and opportunity in a wide variety of fields, including traffic management, urban mobility, security and healthcare. This project presents a scalable miniature implementation of an IoT‐based smart city model, using three physical nodes that perform air quality monitoring, parking sensing, and fire detection. The nodes communicate with a centralised server using NB‐IoT and CoAP protocols. The data ingested from said nodes is stored and visualised using InfluxDB and Grafana. The project evaluates the system from different perspectives, such as integration, load, and battery consumption. Integration testing indicated that all system components integrate properly with each other. Load testing demonstrated that the system can handle a reasonable number of requests without performance degradation. Battery consumption tests indicate that the physical nodes’ battery life lasts for several days. Description: B.Sc. (Hons)(Melit.) Sun, 01 Jan 2023 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/131928 2023-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/124754 Title: Toward a standardized way for reporting on energy efficiency in the metro area network Abstract: Energy is converted from one form to another through the activity of physical processes. The study of energy use, as it is converted from one form to another, therefore necessarily requires detailed understanding of the laws of physics that describe the behaviour of the entity responsible for the conversion (component: level 1 complexity). The complexity of the problem grows rapidly when these fundamental laws are not the ordinary means by which the behaviour of the entity is understood. This condition is common in systems: such aggregates encapsulate the behaviour of their components and obtain physical processes that are functions of the internal organization of these components (system of components: level 2 complexity). The complexity of the problem is compounded further when the ordinary means of interaction with the entity are no longer physical and material, but parametric representations of the entity’s function(s). These representations might be summarized as key performance indices; a more granular knowledge of the entity’s energy use may be obtained through study of the behaviour of its functions under a variety of operating conditions (multi-layered system of components: level 3 complexity). A fourth level in the hierarchy of complexity emerges with a localized system of systems; the fifth and final level of complexity is that of the geographically-dispersed system of systems. The complexity of the study of energy use by telecommunications networks falls into this fifth level. Several problems take root in this complexity. Diversity of components; diversity of systems; diversity of architectures; laxity in terminology; diversity of players, each interested in specific roles and layers, and abuse of abstractions are just some of the highly impactful ones. These problems lead to poorly defined studies of energy use, incorrect cross-comparison of studies, weak analytical technique and over-extrapolated prognoses. It must be conceded that, notwithstanding grave limitations, these works have sown interest in the field and spurred research into better methods. Perhaps this is a common trajectory in the development of our scientific knowledge of this wonderful world. I have primarily addressed the spatial aspect of the problem domain. Seeded by the observed laxity in architectural description and terminology, and driven by a documented failure arising out of misunderstanding of architectures, I have modelled the access portion of the metro area network in sufficient detail to support coherent analysis. Study was restricted to the metro area of the telecommunications network, as this was found to be the extent within a globally-spanning telecommunications network where fastest traffic growth was predicted. The market has been surveyed and the input gathered has been applied to validate my understanding, correct it, and to establish a firm foundation for future cycles of architecturally rigorous descriptions in support of the energy analyst. This work develops mutual understanding between industrial and academic practitioners in two disciplines: sustainability in ICT, and telecommunications operations. The two groups have been approaching one another over the past ten – fifteen years, and much effort has been put in by both sides to cooperate. Sustainability researchers want to reduce telecommunications’ Scope 1 (and beyond) greenhouse gas emissions; moreover, telecommunications network operators are keen to minimize the significant impact that energy use has on their operational expenditure. However, sustainability researchers have been hindered by the complexity of the object of their study, by the immaturity of methods, by the lack of methodology, and it is only recently that some consensus has emerged on good practice and the actual size of the problem (which, in the 1 – 2 % range of GHG emissions, is well short of more dire anticipations). On the other hand, while the operators are willing to share judiciously crafted questions, the detail of network architecture is not a matter of the public domain. The desire for rapprochement is there, but the modus operandi is still somewhat elusive. This work offers a contribution towards a solution of this problem. The standardized methodology of the implementational model has been applied to map the access network, and work is in progress to describe aggregation and metro-core. The models can be integrated with the software-defined networking paradigm. Since the implementational model describes functions and locates them relative to reference points, then it can be used within controllers to interact with service functions in the data plane. The prerequisite is standardized application programming interfaces, and standardized data models that incorporate energy and/or power usage. The former role can be fulfilled by NETCONF (RFC 6241); the latter role can be fulfilled by YANG (RFC 6020), but a valid contender for the latter role is the Green Abstraction Layer (ES 203 237, ES 203 682). The Green Abstraction Layer’s potential is investigated and its likelihood of adoption in the current data-plan driven exchange of link-state data is found to be poor. Regardless of whether GAL or YANG fulfil NETCONF’s content and operations layers, the energy-related notification data in the content layer cannot be generated without real-time power use models, as virtualization containers are not amenable to direct measurement of power use. The field of models is surveyed in a novel manner and contentious problems, productive approaches and significant developments are elicited. Description: Ph.D.(Melit.) Sun, 01 Jan 2023 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/124754 2023-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/124011 Title: Development of a piezoelectric micromachined ultrasonic transducer optimised to operate in the pore solution of reinforced concrete structures Abstract: Structural Health Monitoring (SHM) of Reinforced Concrete (RC) is important to ensure that necessary interventions on concrete structures are conducted in a timely manner. Structural integrity may be effected by various chemical substances such as chloride ions which ingress the concrete’s pore structure and corrode the rebar. Timely detection of such chemical substances and subsequent intervention can avoid potential structural deterioration with ensuing potentially disastrous consequences. The conduct of an effective Structural Health Monitoring regime on civil engineering structures such as bridge decks, can be challenging due to inherent difficulties required to access specific, inaccessible parts of the structure, such as the underside of a bridge deck. This points to the setup of a SHM system, through a microscale distributed sensor network as being an effective proposition. Such a system can be made up of Micro Electromechanical Systems (MEMS) devices. The sensory elements forming the distributed network would be embedded within the concrete structure during the construction phase. To achieve a durable system which is also easy to install during the structure’s construction phase, communication between the sensory elements would need to be conducted through wireless means. This dissertation explored the possibility of using microscale ultrasonic transducers as a means of implementing the inter device wireless communication channel required to achieve a viable distributed sensor system. This work’s primary contribution to the body of knowledge was therefore the development of the devices required to build the ultrasonic transmission path required to form the wireless communication channel. It needs to be clear that while the author has conducted prior work focusing on the sensory part of the system and also published papers in fields such as, the use of galvanic methods for detecting chloride ion ingress, research on the sensory system itself does not form part of this dissertation. Reviewed literature indicated that for microscale ultrasonic devices to operate within an RC structure, two particular components needed to be considered. Firstly, liquid coupling was needed to effectively couple the transducer to the concrete structure. Secondly the frequency of the PMUTs’ operation needed to be in the region of 100 kHz and below. The focus of this dissertation was therefore the development of Piezoelectric Micromachined Ultrasonic Transducers (PMUTs) optimised to operate inside a liquid coupling fluid at this particular frequency range. This was found to be an area in which very sparse background research had been conducted and therefore it must be said that the nature of most of the research conducted in this dissertation was novel. This makes this dissertation a valuable tool which can act as an important background to other researchers in fields involving PMUTs deployed in liquid coupling fluids. Applications that may potentially utilise such technology are not limited to civil engineering but also encompasses areas such as the biomedical and marine engineering fields. This dissertation outlines the extensive analytical, Finite Element Modelling (FEM) and experimental work conducted to explore the dynamics of PMUT design and operation. This included studies conducted with various variables being modified such as, filling the PMUT cavity with gas or liquid, the utilisation of different excitation frequencies, and also the utilisation of coupling fluids having different densities such as isopropanol or glycerine. Furthermore this dissertation also presents the development of various novel PMUT designs which were found to provide enhancements in ultrasonic reception or transmission performance. Such enhancements were based on designs such as multi electrode patterns and modified diaphragm structures. The devices developed in this dissertation were based on the PiezoMUMPSTM Multi Project Wafer (MPW) design concept. Aluminium nitride was used as the piezoelectric material found at the core of the devices’ operational dynamics. Description: Ph.D.(Melit.) Sun, 01 Jan 2023 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/124011 2023-01-01T00:00:00Z