Rigorous Design of Fault-Tolerant Transactions for Replicated Database Systems using Event B

System availability is improved by the replication of data objects in a distributed database system. However, during updates, the complexity of keeping replicas identical arises due to failures of sites and race conditions among conflicting transactions. Fault tolerance and reliability are key issues to be addressed in the design and architecture of these systems. Event B is a formal technique which provides a framework for developing mathematical models of distributed systems by rigorous description of the problem, gradually introducing solutions in refinement steps, and verification of solutions by discharge of proof obligations. In this paper, we present a formal development of a distributed system using Event B that ensures atomic commitment of distributed transactions consisting of communicating transaction components at participating sites. This formal approach carries the development of the system from an initial abstract specification of transactional updates on a one copy database to a detailed design containing replicated databases in refinement. Through refinement we verify that the design of the replicated database confirms to the one copy database abstraction

An incremental development of the Mondex system in Event-B

A development of the Mondex system was undertaken using Event-B and its associated proof tools. An incremental approach was used whereby the refinement between the abstract specification of the system and its detailed design was verified through a series of refinements. The consequence of this incremental approach was that we achieved a very high degree of automatic proof. The essential features of our development are outlined. We also present some modelling and proof guidelines that we found helped us gain a deep understanding of the system and achieve the high degree of automatic proo

Rigorous Design of Distributed Transactions

Database replication is traditionally envisaged as a way of increasing fault-tolerance and availability. It is advantageous to replicate the data when transaction workload is predominantly read-only. However, updating replicated data within a transactional framework is a complex affair due to failures and race conditions among conflicting transactions. This thesis investigates various mechanisms for the management of replicas in a large distributed system, formalizing and reasoning about the behavior of such systems using Event-B. We begin by studying current approaches for the management of replicated data and explore the use of broadcast primitives for processing transactions. Subsequently, we outline how a refinement based approach can be used for the development of a reliable replicated database system that ensures atomic commitment of distributed transactions using ordered broadcasts. Event-B is a formal technique that consists of describing rigorously the problem in an abstract model, introducing solutions or design details in refinement steps to obtain more concrete specifications, and verifying that the proposed solutions are correct. This technique requires the discharge of proof obligations for consistency checking and refinement checking. The B tools provide significant automated proof support for generation of the proof obligations and discharging them. The majority of the proof obligations are proved by the automatic prover of the tools. However, some complex proof obligations require interaction with the interactive prover. These proof obligations also help discover new system invariants. The proof obligations and the invariants help us to understand the complexity of the problem and the correctness of the solutions. They also provide a clear insight into the system and enhance our understanding of why a design decision should work. The objective of the research is to demonstrate a technique for the incremental construction of formal models of distributed systems and reasoning about them, to develop the technique for the discovery of gluing invariants due to prover failure to automatically discharge a proof obligation and to develop guidelines for verification of distributed algorithms using the technique of abstraction and refinement

Formal Development of Fault Tolerant Transactions for a replicated Database using Ordered Broadcasts

Data replication across several sites improves fault tolerance as available sites can take over the load of failed sites. Data is usually accessed within a transactional framework. However, updating replicated data within a transactional framework is a complex affair due to failures and conflicting transactions. Group communication primitives have been proposed to support transactions in a asynchronous distributed system. In this paper we outline how a refinement based approach with Event B can be used for the development of a reliable replicated database system that ensure atomic commitment of update transactions using group communication primitives

Rigorous design of distributed transactions

Database replication is traditionally envisaged as a way of increasing fault-tolerance and availability. It is advantageous to replicate the data when transaction workload is predominantly read-only. However, updating replicated data within a transactional framework is a complex affair due to failures and race conditions among conflicting transactions. This thesis investigates various mechanisms for the management of replicas in a large distributed system, formalizing and reasoning about the behavior of such systems using Event-B. We begin by studying current approaches for the management of replicated data and explore the use of broadcast primitives for processing transactions. Subsequently, we outline how a refinement based approach can be used for the development of a reliable replicated database system that ensures atomic commitment of distributed transactions using ordered broadcasts. Event-B is a formal technique that consists of describing rigorously the problem in an abstract model, introducing solutions or design details in refinement steps to obtain more concrete specifications, and verifying that the proposed solutions are correct. This technique requires the discharge of proof obligations for consistency checking and refinement checking. The B tools provide significant automated proof support for generation of the proof obligations and discharging them. The majority of the proof obligations are proved by the automatic prover of the tools. However, some complex proof obligations require interaction with the interactive prover. These proof obligations also help discover new system invariants. The proof obligations and the invariants help us to understand the complexity of the problem and the correctness of the solutions. They also provide a clear insight into the system and enhance our understanding of why a design decision should work. The objective of the research is to demonstrate a technique for the incremental construction of formal models of distributed systems and reasoning about them, to develop the technique for the discovery of gluing invariants due to prover failure to automatically discharge a proof obligation and to develop guidelines for verification of distributed algorithms using the technique of abstraction and refinement.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Rigorous Design of Fault Tolerance and Recovery Algorithm for Disaster Management and Relief Distribution System using Event-B

518-529India is vulnerable to disasters such as earthquakes, floods, tsunamis, landslides forest fires and cyclones due to its unique socio-economic and geo-climatic conditions. Twenty seven out of thirty-six states and union territories are prone to different types of disasters which cause loss of life, disruption of livelihoods, damage to infrastructure and property which in turn becomes a heavy burden on the national economy. Effective management of relief work is a key step towards normalizing human life post disaster. In this paper, we have presented the formal development and verification of a fault tolerance and recovery algorithm for district level disaster control centers in India which are connected to each other via a communication network. Formal methods help in the verification of critical properties of complex systems by developing mathematical models so that design errors can be detected and removed during the early stages of software development. Event-B, which is a formal method and Rodin platform is used for this work. Event-B is a mathematical language of first-order logic to provide a solution to the complex algorithms formally. In this algorithm a Disaster Control Centre is chosen as the coordinator based on its unique vote value. This vote value is allotted and modified dynamically based on the extent of damage in the area where the center is located. The center having the highest vote value among the currently active centers is elected as the coordinator. The correctness of the algorithm is verified through discharge of proof obligations generated by the Event-B model

Formal Verification of Receiver Initiated Load Distribution Protocol with Fault Tolerance and Recovery using Event-B

1078-1090Load distribution is a process that involves the allocation of tasks to various nodes in the distributed system in such a manner that overall resource utilization is maximized, and overall response time is minimized. This paper presents a formal model for verification of receiver-initiated load balancing and fault tolerance protocol with recovery in distributed systems using the eclipse-based Event-B platform called Rodin. Here, the receiver-initiated load balancing approach is demonstrated along with tolerance of node failure and recovery. In this approach, an underloaded node (receiver) initiates the process of load transfer from an overloaded node (sender). The underloaded node broadcasts a request message to obtain load from the overloaded nodes. The overloaded nodes reply with their load value. The underloaded node then selects the optimal overloaded node for load transfer. The chances of node failure are minimized by reducing the number of overloaded nodes. The process of recovery from failure is also shown in the proposed model. Formal methods are used to mathematically verify the critical properties of the system by developing a model based on its specifications. Our objective is to verify and validate the model for correctness through discharge of proof obligations using Event-B. Event-B is a formal method which is used for verification of a model based on distributed systems. The proof obligations generated by the model are discharged which ensures the correctness of our model

Text Summarization Technique for Punjabi Language Using Neural Networks

In the contemporary world, utilization of digital content has risen exponentially. For example, newspaper and web articles, status updates, advertisements etc. have become an integral part of our daily routine. Thus, there is a need to build an automated system to summarize such large documents of text in order to save time and effort. Although, there are summarizers for languages such as English since the work has started in the 1950s and at present has led it up to a matured stage but there are several languages that still need special attention such as Punjabi language. The Punjabi language is highly rich in morphological structure as compared to English and other foreign languages. In this work, we provide three phase extractive summarization methodology using neural networks. It induces compendious summary of Punjabi single text document. The methodology incorporates pre-processing phase that cleans the text; processing phase that extracts statistical and linguistic features; and classification phase. The classification based neural network applies an activation function- sigmoid and weighted error reduction-gradient descent optimization to generate the resultant output summary. The proposed summarization system is applied over monolingual Punjabi text corpus from Indian languages corpora initiative phase-II. The precision, recall and F-measure are achieved as 90.0%, 89.28% an 89.65% respectively which is reasonably good in comparison to the performance of other existing Indian languages" summarizers.This research is partially funded by the Ministry of Economy, Industry and Competitiveness, Spain (CSO2017-86747-R)

Automatic Text Summarization for Hindi Using Real Coded Genetic Algorithm

In the present scenario, Automatic Text Summarization (ATS) is in great demand to address the ever-growing volume of text data available online to discover relevant information faster. In this research, the ATS methodology is proposed for the Hindi language using Real Coded Genetic Algorithm (RCGA) over the health corpus, available in the Kaggle dataset. The methodology comprises five phases: preprocessing, feature extraction, processing, sentence ranking, and summary generation. Rigorous experimentation on varied feature sets is performed where distinguishing features, namely- sentence similarity and named entity features are combined with others for computing the evaluation metrics. The top 14 feature combinations are evaluated through Recall-Oriented Understudy for Gisting Evaluation (ROUGE) measure. RCGA computes appropriate feature weights through strings of features, chromosomes selection, and reproduction operators: Simulating Binary Crossover and Polynomial Mutation. To extract the highest scored sentences as the corpus summary, different compression rates are tested. In comparison with existing summarization tools, the ATS extractive method gives a summary reduction of 65%