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PhD / Many popular database management systems implement a multiversion concurrency control algorithm called snapshot isolation rather than providing full serializability based on locking. There are well-known anomalies permitted by snapshot isolation that can lead to violations of data consistency by interleaving transactions that would maintain consistency if run serially. Until now, the only way to prevent these anomalies was to modify the applications by introducing explicit locking or artificial update conflicts, following careful analysis of conflicts between all pairs of transactions. This thesis describes a modification to the concurrency control algorithm of a database management system that automatically detects and prevents snapshot isolation anomalies at runtime for arbitrary applications, thus providing serializable isolation. The new algorithm preserves the properties that make snapshot isolation attractive, including that readers do not block writers and vice versa. An implementation of the algorithm in a relational database management system is described, along with a benchmark and performance study, showing that the throughput approaches that of snapshot isolation in most cases.

Thesis (M.S.)--Humboldt State University, 2007. / Includes bibliographical references (leaves 118-122). Also available via Humboldt Digital Scholar.

The Subtext project seeks to make programming fundamentally easier by altering the nature of programming languages and tools. This paper defines an operational semantics for an essential subset of the Subtext language. It also presents a fresh approach to the problems of mutable state, I/O, and concurrency.Inclusions reify copy & paste edits into persistent relationships that propagate changes from their source into their destination. Inclusions formulate a programming language in which there is no distinction between a program’s representation and its execution. Like spreadsheets, programs are live executions within a persistent runtime, and programming is direct manipulation of these executions via a graphical user interface. There is no need to encode programs into source text.Mutation of state is effected by the computation of hypothetical recursive variants of the state, which can then be lifted into new versions of the state. Transactional concurrency is based upon queued single-threaded execution. Speculative execution of queued hypotheticals provides concurrency as a semantically transparent implementation optimization.

Magister Legum - LLM

ACette thèse s’intéresse à l’étude des modèles de transactions plates et étendues dans les SGBD temps réel (SGBDTR). Ce travail est réalisé en deux étapes : (i) la première étape vise à aider les concepteurs à décrire et comparer les modèles de transactions temps réel, (ii) La seconde étape permet de compléter cette étude par la présentation d’une étude stochastique des performances des SGBDTR de deux modèles de transactions temps réel, à savoir le modèle de transactions plates et le modèle de transactions emboîtées. Dans la première étape, nous avons présenté le méta-modèle « MRT-ACTA » qui prend en compte les caractéristiques temporelles des transactions et de données temps réel ainsi que leurs interactions, offrant ainsi aux concepteurs la possibilité de définir de nouveaux modèles de transactions temps réel et de les comparer. La description formelle de « M-RT-ACTA » a permis de valider nos propositions. Pour compléter ce travail et ayant constaté que l’ordonnancement des transactions est un aspect primordial dans les SGBDTR, nous avons proposé dans la seconde étape de présenter une étude stochastique des performances des SGBDTR. Ainsi, nous avons proposé une amélioration des taux de succès des transactions plates avec le protocole GEDF (généralisation de EDF) et nous avons adapté cette étude aux transactions emboîtées. / This thesis presents a study of flat and extended model of transactions in real-time DBMS (RTDBMSs). This study is carried in two steps : (i) the first step aims to help designers to describe and compare models of real-time transactions, (ii) the second step allows to complete this study by presenting a stochastic study of RTDBMSs performance using two models of real-time transactions : flat transactions and nested transactions models. In the first step, we introduced the meta-model « MRT-ACTA » that takes into account the transactions and data temporal characteristics and their realtime interactions. « M-RT-ACTA » allows designers defining and comparing new models of real-time transactions. The formal description of « M-RT-ACTA » validates our proposals. In order to complete this work, we have observed that transactions scheduling is an important area in RTDBMSs, so we proposed in the second step a stochastic study of RTDBMS performance. Thus, we have proposed to improve the success ratio of flat transactions with GEDF protocol (generalization of GEDF) and we have adapted this study to nested transactions.

This project uses system engineering and system management principles to analyze the problem of transactions in Nigerian universities and tertiary institutions. System management principles shall be used to highlight the imperfections in the transaction method currently in use especially the disconnect between the bank and the institutions using their services. It will explore other payment systems available in the country. This project will provide a recommendation of how to implement a better payment option through automating the process of school payments by using a system with a cloud-based educational software at the school bursary office and through the online payment processing on the school website. The system software will enable cashiering and payment management: centralized data, automated reports, and inventory controls. It will generate automatic invoices and receipts. This system will bridge the disconnect between the bank and the school since students would not need to deposit cash directly into the school account but into their accounts and then pay with their debit cards. The system will provide debit card encryption and protection using the Secure Socket Layer technology.

It is a settled principle in our tax law that a court will not be deceived by the form of a transaction, but that effect will be given to the true substance thereof. This principle, embodied in the common law doctrine of substance over form, has been affirmed and applied by the judiciary for well over a century, especially in matters where taxpayers avoid the imposition of potential tax through simulating their transactions. If a court was satisfied that the parties subjectively intended to give effect to some other agreement between them, the court would only have regard to the actual rights and obligations created by the parties and impose tax on their real transactions in accordance with the provisions of a taxing statute. The law in respect of simulated transactions was clear. However, in Commissioner for the South African Revenue Service v NWK Ltd [2011 (2) SA 67 (SCA)] the court ostensibly introduced the requirement of commercial substance as a criterion to determine simulation. The requirement postulates that a transaction which lacks commercial substance will be regarded as simulated, irrespective of the parties’ genuine intention to give effect to the agreement between them. The requirement appears to overrule the entrenched test under the common law doctrine of substance over form and ostensibly established a new objective, independent common law criterion to determine simulation. The NWK requirement invariably ventures into the sphere of legitimate tax planning by virtue of its wide-ranging nature. Taxpayers need to understand the boundaries within which they may legitimately structure their affairs to reduce a potential tax burden as this advances the predictability of the law and respects the rule of law. NWK has, however, rendered the law on this subject rather uncertain and it is therefore crucial to establish the effect and applicability of the requirement to provide guidance to taxpayers on how to structure their affairs to legitimately avoid tax. The question, therefore, is whether the requirement is capable of independent application to determine simulation, or whether the requirement is only indicative of the presence of simulation in a transaction? If the latter, the common law position prior to the judgment will continue to prevail. In this dissertation, compelling arguments which illustrate the incapability of the requirement to function independently to determine simulation is researched, analysed and advanced. These arguments support the view that from a legal and logical point of view, the requirement cannot constitute an independent criterion to determine simulation. In the premise, it is submitted that the established common law doctrine of substance over form, as enunciated in Zandberg v Van Zyl [1910 AD 302], remains reflective of the law on simulated transactions and that the commercial substance requirement is only indicative of the presence of possible simulation in a transaction. / Dissertation (LLM)--University of Pretoria, 2013. / am2014 / Mercantile Law / unrestricted

One of the main trends in the IT field today is to provide more mobility to existing IT based systems and users. With this trend, more and more people are using mobile financial transactions due to a widespread proliferation of mobile phones and wireless technologies. One of the most important concerns with such transactions is their security. The reasons are based on weaknesses of wireless protocols and additional requirements for handling of financial data. These aspects make mobile financial transactions and applications even more vulnerable to fraud and illegal use than similar transactions performed over fixed networks.   There are two important aspects related to security in mobile environments. First, security features provided by the communication protocols, such as GSM, SMS, Bluetooth, Mobile Internet, etc. are not adequate. Some security algorithms used by these protocols have even been broken, what requires upper layer applications to provide comprehensive protection in order to compensate the shortcomings of a transportation layer. Second, mobile devices have limited capabilities, limited processing speed, limited storage, etc, so that many security mechanisms are not suitable for mobile environments. Therefore, new, effective, lightweight and flexible security solutions are required.   In order to solve these two groups of security issues, in this research we created a service-oriented security infrastructure for mobile financial transactions and applications. Based on this infrastructure, we also designed and implemented a system, which is called SAFE (Secure Applications for Financial Environment), that represents a secure, convenient and reliable large–scale infrastructure for mobile financial transactions. The components of the system are Secure Mobile Wallet and three SAFE servers: Communications (Gateway) Server, IDMS (Identity Management System) Server, and Payment Server. Those core infrastructure components with secure messages exchanged between them provide a number of secure financial services. These services may be used for various types of mobile transactions: m–Banking, m–Commerce, m–Ticketing, m-Parking, m–Loans, etc. all supported by additional Application Services Provider servers, connected to the SAFE security system. This report gives the details of the concept design and current implementation of the SAFE system. / QC20100608 / Secure Applications for Financial Environments (SAFE) Project

The study of shared memory concurrency is extensive. There exist many state-of-the-art strategies for dealing with fundamental concurrency problems, such as race conditions or deadlocks, to leverage massive performance boosts out of modern multiprocessors. With the introduction of blockchain technology as a popular financial tool, we observe many decades-old concurrency problems re-emerge within the context of decentralized networks. These challenges introduce additional constraints, such as the lack of hardware atomic instructions like Compare-And-Swap, or the potential for malicious clients to join the network. In this dissertation, we propose key algorithms which adapt knowledge from the domain of shared memory concurrency to solve emerging concurrency problems in decentralized networks. We propose three key algorithms which further the state of the art in decentralized networks. (1) We present Hash-Mark-Set, a concurrent algorithm for providing a read-uncommitted view of the blockchain state, enabling a higher success rate in transaction use cases where state changes frequently in relation to the block interval. (2) We propose Proof of Descriptor, a descriptor based consensus mechanism for decentralized networks. Proof of Descriptor utilizes well-known techniques from shared memory concurrent programming to create an efficient and scalable algorithm for blockchain consensus. (3) We propose a descriptor-based algorithm for concurrent execution of smart contracts that efficiently captures the concurrent execution as a graph of descriptors, enabling validators to analyze the concurrent execution and verify its results through re-execution.