The focus of this dissertation is on large-scale and long-running networked real-time multiplayer games. In this type of games, each player controls one or many entities, which interact in a shared virtual environment. Three attributes - scalability, security, and fault tolerance - are considered essential for this type of games. The normal approaches for building this type of games, using a client/server or peer-to-peer architecture, fail in achieving all three attributes. We propose a server-network architecture that supports these attributes. In this architecture, a cluster of servers collectively manage the game state and each server manages a separate region of the virtual environment. We discuss how the architecture can be extended using proxies, and we compare it to other similar architectures. Further, we investigate how a distributed database management system can support the proposed architecture. Since efficiency is very important in this type of games, some properties of traditional database systems must be relaxed. We also show how methods for increasing scalability, such as interest management and dead reckoning, can be implemented in a database system. Finally, we suggest how the proposed architecture can be validated using a simulation of a large-scale game.

In this dissertation, we consider the problem of recovering a crashed node in a distributed database. We especially focus on real-time recovery in eventually consistent databases, where the consistency of replicated data is traded off for increased predictability, availability and performance. To achieve this focus, we consider consistency preservation techniques as well as recovery mechanisms. Our approach is to perform a thorough literature survey of these two fields. The literature survey considers not only recovery in real-time, distributed, eventually consistent databases, but also related techniques, such as recovery in main-memory resident or immediately consistent databases. We also examine different techniques for consistency preservation. Based on this literature survey, we present a taxonomy and state-of-the-art report on recovery mechanisms and consistency preservation techniques. We contrast different recovery mechanisms, and highlight properties and aspects of these that make them more or less suitable for use in an eventually consistent database. We also identify unexplored areas and uninvestigated problems within the fields of database recovery and consistency preservation. We find that research on real-time recovery in distributed databases is lacking, and we also propose further investigation of how the choice of consistency preservation technique affects (or should affect) the design of a recovery mechanism for the system.

Databases nowadays used in all kinds of application areas often differ greatly in a number of properties. These varieties add complexity to the handling of databases, especially when two or more different databases are dependent. The approach described here to propagate updates in an application scenario with heterogeneous, dependent databases is the use of a rule-based mediator. The system EruS (ECA rules updating SCOP) applies active database technologies in a bioinformatics scenario. Reactive behaviour based on rules is used for databases holding protein structures. The inherent heterogeneities of the Structural Classification of Proteins (SCOP) database and the Protein Data Bank (PDB) cause inconsistencies in the SCOP data derived from PDB. This complicates research on protein structures. EruS solves this problem by establishing rule-based interaction between the two databases. The system is built on the rule engine ruleCore with Event-Condition-Action rules to process PDB updates. It is complemented with wrappers accessing the databases to generate the events, which are executed as actions. The resulting system processes deletes and modifications of existing PDB entries and updates SCOP flatfiles with the relevant information. This is the first step in the development of EruS, which is to be extended in future work. The project improves bioinformatics research by providing easy access to up-to-date information from PDB to SCOP users. The system can also be considered as a model for rule-based mediators in other application areas.

This thesis, that comes together with an extranet and internet site programmed in ASP.NET 2.0, has been written in the context of our final project on bachelor level in association with the School of Engineering – Jönköping University. We had the choice to think of a project on our own or to work in association with a company. As the Belgian company Induma came with this idea, we decided to work this project out. Our project has got the name ‘Company Communication System for Customers and Dealers’. Besides the front-end and back-end internet site, it will also include a system for customers and dealers, extranet site. So the site will get more interactive and there will be more online transactions possible. We would like to thank the School of Engineering – Jönköping University, KATHO – VHTI and our parents to get the chance to experience studying abroad. We would also like to thank the company Induma for their cooperation and our Belgian and Swedish supervisors K. Deseyne and M. Schoultz for their guidance and help.

Distributed real-time databases can be used to support data sharing for applications in wireless ad-hoc networks. In such networks, topology changes frequently and partitions may be unpredictable and last for an unbounded period. In this thesis, the existing database replication protocol PRiDe is extended to handle such long-lasting partitions. The protocol uses optimistic and detached replication to provide predictable response times in unpredictable networks and forward conflict resolution to guarantee progress. The extension, pPRiDe, combines update and state transfer strategies. Update transfer for intra-partition communication can reduce bandwidth usage and ease conflict resolution. State transfer for inter partition conflicts removes dependency on a common state between partitions prior to the merge to apply update messages on. This makes the resource usage independent of the life span of partitions. This independence comes at the cost of global data stability guarantees and pPRiDe can thus only provide per partition guarantees. The protocol supports application specific conflict resolution routines for both state and update conflicts. A basic simulator for mobile ad-hoc networks has been developed to validate that pPRiDe provides eventual consistency. pPRiDe shows that a hybrid approach to change propagation strategy can be beneficial in networks where collaboration by data sharing within long lasting partitions and predictable resource usage is necessary. These types of systems already require the conflict management routines necessary for pPRiDe and can benefit from an existing protocol. In addition to pPRiDe and the simulator this thesis provides a flexible object database suitable for future works and an implementation of PRiDe on top of that database.

Title:Comparison of databases – Is the law an obstacle? Authors:Alexander Ankarberg, Applied Information Science. Tutors:Lars- Eric Ljung Problem: Cross running databases is getting more and more significant during the development of the information flow. There are huge benefits if we start to use the technique that already exists. The law is today an obstacle, so what would happen if the law wasn’t so stern. My question is:” why don’t we cross run databases more efficient between parts of institutions” Aim:The purpose of this essay is to evaluate why institutions does not cross run databases and start a discussion. There are possibilities that we today does not use. One aim is also to find solutions so that we can start to use the techniques. The essay will explain the fundamentals and discuss both the advantages and the disadvantages in depth. Method:The author has approached the problem from two ways. From induction and deduction which combined is abduction. The author hopes that this results in as many points of angles as possible. And the answers will be as complete as possible. The essay also includes an inquiry which is based on interview with ordinary people. Conclusions:The law is not up to date nor made for today’s technique. It is in some ways an obstacle for a more efficient system and it could save enormous amounts of money for both the government and common man. There is hope though, and small revolutions happen every day. There is also ways to go around the law and make things possible and make the system more efficient. That is with agreement from the person that the information is about. There is also one possibility with safety classes, to put a number on information.

There is a need of storing and keeping track of things. As the amount of information increases, so does the demand for suitable applications that can manage the data. This thesis has had its focus on developing a web administration interface for relational databases, where the focus has been on managing and visualizing the data, where relationships between data within the database could be predicted through an algorithm. During the thesis, it was revealed that administrators can utilize naming conventions for databases, a property which can be used to predict its relationships. Furthermore, existing applications for managing databases has been compared with the thesis' implementation. Notable differences are that existing solutions are focused towards the structure of the data, rather than the data itself. To accomplish all this, an agile method was chosen for fast results within the deadline, together with standardized web development tools and JavaScript frameworks. The resulting implementation consists of a front- and backend. The frontend was developed using the Ember.JS framework for making web applications and the backend was implemented using Node.JS, together with a component for handling different database dialects called Sequelize. It has been concluded that the prototype this thesis has resulted in works as a proof of concept, complete with a prediction algorithm that can suggest relationships within databases that utilizes convenient and consistent naming conventions. In the future, further research and tests could be conducted to evaluate the security, reliability and usability of the application, to ensure its production quality.

Context: Determining attribute correspondence is the most important, time consuming and knowledge intensive part during databases integration. It is also used in other data manipulation applications such as data warehousing, data design, semantic web and e-commerce. Objectives: In this thesis the aim is to investigate how to find the types of correspondence between the attributes of heterogeneous datasets when schema design information of the data sets is unknown. Methods: A literature review was conducted to extract the knowledge related to the approaches that are used to find the correspondence between the attributes of heterogeneous datasets. Extracted knowledge from the literature review is used in developing an instance based approach for finding types of correspondence between the attributes of heterogeneous datasets when schema design information is unknown. To validate the proposed approach an experiment was conducted in the real environment using the data provided by the Telecom Industry (Ericsson) Karlskrona. Evaluation of the results was carried using the well known and mostly used measures from information retrieval field precision, recall and F-measure. Results: To find the types of correspondence between the attributes of heterogeneous datasets, good results depend on the ability of the algorithm to avoid the unmatched pairs of rows during the Row Similarity Phase. An evaluation of proposed approach is performed via experiments. We found 96.7% (average of three experiments) F-measure. Conclusions: The analysis showed that the proposed approach was feasible to be used and it provided users a mean to find the corresponding attributes and the types of correspondence between corresponding attributes, based on the information extracted from the similar pairs of rows from the heterogeneous data sets where their similarity based on the same common primary keys values.

Ces dernières années ont vu un regain d’intérêt dans l’utilisation de données semi-structurées, grâce à la standardisation de formats d’échange de données sur le Web tels que XML et RDF. On notera en particulier le Linking Open Data Project qui comptait plus de 31 milliard de triplets RDF à la fin de l’année 2011. XML reste, pour sa part, l’un des formats de données privilégié de nombreuses bases de données de grandes tailles dont Uniprot, Open Government Initiative et Penn Treebank. <p><p>Cet accroissement du volume de données semi-structurées a suscité un intérêt croissant pour le développement de bases de données adaptées. Parmi les différentes approches proposées, on peut distinguer les approches relationnelles et les approches graphes, comme détaillé au Chapitre 3. Les premières visent à exploiter les moteurs de bases de données relationnelles existants, en y intégrant des techniques spécialisées. Les secondes voient les données semistructurées comme des graphes, c’est-à-dire un ensemble de noeuds liés entre eux par des arêtes étiquetées, dont elles exploitent la structure. L’une des techniques de ce domaine, connue sous le nom d’indexation structurelle, vise à résumer les graphes de données, de sorte à pouvoir identifier rapidement les données utiles au traitement d’une requête.<p><p>Les index structurels classiques sont construits sur base des notions de simulation et de bisimulation sur des graphes. Ces notions, qui sont d’usage dans de nombreux domaines tels que la vérification, la sécurité, et le stockage de données, sont des relations sur les noeuds des graphes. Fondamentalement, ces notions caractérisent le fait que deux noeuds partagent certaines caractéristiques telles qu’un même voisinage. <p><p>Bien que les approches graphes soient efficaces en pratique, elles présentent des limitations dans le cadre de RDF et son langage de requêtes SPARQL. Les étiquettes sont, dans cette optique, distinctes des noeuds du graphe .Dans le modèle décrit par RDF et supporté par SPARQL, les étiquettes et noeuds font néanmoins partie du même ensemble. C’est pourquoi, les approches graphes ne supportent qu’un sous-ensemble des requêtes SPARQL. Au contraire, les approches relationnelles sont fidèles au modèle RDF, et peuvent répondre au différentes requêtes SPARQL. <p><p>La question à laquelle nous souhaitons répondre dans cette thèse est de savoir si les approches relationnelles et graphes sont incompatible, ou s’il est possible de les combiner de manière avantageuse. En particulier, il serait souhaitable de pouvoir conserver la performance des approches graphe, et la généralité des approches relationnelles. Dans ce cadre, nous réalisons un index structurel adapté aux données relationnelles. <p><p>Nous nous basons sur une méthodologie décrite par Fletcher et ses coauteurs pour la conception d’index structurels. Cette méthodologie repose sur trois composants principaux. Un premier composant est une caractérisation dite structurelle du langage de requêtes à supporter. Il s’agit ici de pouvoir identifier les données qui sont retournées en même temps par n’importe quelle requête du langage aussi précisément que possible. Un second composant est un algorithme qui doit permettre de grouper efficacement les données qui sont retournées en même temps, d’après la caractérisation structurelle. Le troisième composant est l’index en tant que tel. Il s’agit d’une structure de données qui doit permettre d’identifier les groupes de données, générés par l’algorithme précédent pour répondre aux requêtes. <p><p>Dans un premier temps, il faut remarquer que le langage SPARQL pris dans sa totalité ne se prête pas à la réalisation d’index structurels efficaces. En effet, le fondement des requêtes SPARQL se situe dans l’expression de requêtes conjonctives. La caractérisation structurelle des requêtes conjonctives est connue, mais ne se prête pas à la construction d’algorithmes efficaces pour le groupement. Néanmoins, l’étude empirique des requêtes SPARQL posées en pratique que nous réalisons au Chapitre 5 montre que celles-ci sont principalement des requêtes conjonctives acycliques. Les requêtes conjonctives acycliques sont connues dans la littérature pour admettre des algorithmes d’évaluation efficaces. <p><p>Le premier composant de notre index structurel, introduit au Chapitre<p>6, est une caractérisation des requêtes conjonctives acycliques. Cette<p>caractérisation est faite en termes de guarded simulation. Pour les graphes la<p>notion de simulation est une version restreinte de la notion de bisimulation.<p>Similairement, nous introduisons la notion de guarded simulation comme une<p>restriction de la notion de guarded bisimulation, une extension connue de la<p>notion de bisimulation aux données relationelles. <p><p>Le Chapitre 7 offre un second composant de notre index structurel. Ce composant est une structure de données appelée guarded structural index qui supporte le traitement de requêtes conjonctives quelconques. Nous montrons que, couplé à la caractérisation structurelle précédente, cet index permet d’identifier de manière optimale les données utiles au traitement de requêtes conjonctives acycliques. <p><p>Le Chapitre 8 constitue le troisième composant de notre index structurel et propose des méthodes efficaces pour calculer la notion de guarded simulation. Notre algorithme consiste essentiellement en une transformation d’une base de données en un graphe particulier, sur lequel les notions de simulation et guarded simulation correspondent. Il devient alors possible de réutiliser les algorithmes existants pour calculer des relations de simulation. <p><p>Si les chapitres précédents définissent une base nécessaire pour un index structurel visant les données relationnelles, ils n’intègrent pas encore cet index dans le contexte d’un moteur de bases de données relationnelles. C’est ce que propose le Chapitre 9, en développant des méthodes qui permettent de prendre en compte l’index durant le traitement d’une requête SPARQL. Des résultats expérimentaux probants complètent cette étude. <p><p>Ce travail apporte donc une première réponse positive à la question de savoir s’il est possible de combiner de manière avantageuse les approches relationnelles et graphes de stockage de données RDF.<p> / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

In the recent years, crowdfunding (a phenomenon where individuals collectively contribute money to back different goals and projects through the internet) has been gaining a lot of attention especially for its socio-economic impact. This dissertation explores this phenomenon in three distinct but related essays. The first essay explores the nature and dynamics of backers’ contributions and uses the insights generated to develop a forecasting model that can predict crowdfunding campaign outcomes. The second essay investigates how creators’ crowdfunding campaign design decisions impact their funding and post-funding outcomes. Interestingly, the essay highlights that certain crowdfunding campaign design decisions have differential effects on both funding and post-funding phases and this has implications for creators, backers, and crowdfunding platform owners. Finally, the third essay investigates whether creators’ post-funding relations-building efforts with backers matter and how such relations-building efforts might impact the performance of their subsequent crowdfunding campaign. In general, this dissertation not only increases our understanding of the crowdfunding phenomenon across the funding and post-funding phases, it also provides insights and tools that can help stakeholders maximize the benefits accruable to them when they engage in crowdfunding.