Proving Correctness of Transformation Functions in Real-Time Groupware

Colloque avec actes et comité de lecture. internationale.International audienceOperational transformation is an approach which allows to build real-time groupware tools. This approach requires correct transformation functions. Proving the correction of these transformation functions is very complex and error prone. In this paper, we show how a theorem prover can address this serious bottleneck. To validate our approach, we have verified the correctness of state-of-art transformation functions defined on Strings with surprising results. Counter-examples provided by the theorem prover have helped us to define new correct transformation functions for Strings

Optimistic replication

Data replication is a key technology in distributed data sharing systems, enabling higher availability and performance. This paper surveys optimistic replication algorithms that allow replica contents to diverge in the short term, in order to support concurrent work practices and to tolerate failures in low-quality communication links. The importance of such techniques is increasing as collaboration through wide-area and mobile networks becomes popular. Optimistic replication techniques are different from traditional “pessimistic ” ones. Instead of synchronous replica coordination, an optimistic algorithm propagates changes in the background, discovers conflicts after they happen and reaches agreement on the final contents incrementally. We explore the solution space for optimistic replication algorithms. This paper identifies key challenges facing optimistic replication systems — ordering operations, detecting and resolving conflicts, propagating changes efficiently, and bounding replica divergence — and provides a comprehensive survey of techniques developed for addressing these challenges

Програмне забезпечення на основі операціональних трансформацій для створення користувацьких додатків

Кваліфікаційна робота включає пояснювальну записку (60 с., 24 рис., 1 табл., 4 додатки). Об’єкт розробки –клієнтське програмне забезпечення на основі технології операціональних трансформацій, яке дозволяє швидко, зручно та безпечно обмінюватись даними будь-якого типу між клієнтом та сервером операціональних трансформацій, передаючи серверу дані та операції у бінарному форматі для подальшого їх зберігання у вигляді графа з комітами. В роботі розроблено програмне забезпечення, а саме вебдодаток для роботи з файловою системою, який дозволяє зберігати та видаляти файли та їх дані. Користувач має змогу працювати зі своєю власною файловою системою з кількох пристроїв одночасно, навіть при тривалій відсутності підключення до мережі. Розроблене клієнтське програмне забезпечення з використанням операціональних трансформацій дозволяє: - надсилати клієнтські запити на віддалений сервер операціональних трансформацій; - перетворювати дані будь-якого типу в бінарний формат та формувати зліпки даних для серверної частини; - вирішувати клієнтські конфлікти даних; - застосовувати основні властивості системи операціональних трансформацій для перетворення кількох операцій ; В ході виконання дипломного проєкту: - розроблено вебдодаток файлової системи на основі ОТ технології; - проведено аналіз існуючих рішень; - розроблено структуру клієнтського ядра операціональних трансформацій.Qualification work includes an explanatory note (60 pages, 24 pictures, 1 table, 4 appendices). The object of development is client software based on operational transformation technology, which allows fast, convenient and secure exchange of data of any type between the client and the operational transformation server, transmitting data and operations to the server in binary format for further storage as a graph of commits. The software has been developed, namely a web application for working with the file system, which allows you to save and delete files and their data. The user can work with his own file system from several devices at the same time, even if there is no network connection for a long time. Developed client software using operational transformations allows: - send client requests to a remote server of operational transformations; - convert data of any type into binary format and form data casts for the server part; - resolve customer data conflicts; - apply the basic properties of the system of operational transformations to transform several operations; During the implementation of the diploma project: - developed a web application of a file system based on OT technology; - the analysis of existing decisions is carried out; - the structure of the client core of operational transformations is developed

Crowdsourcing decision support: frugal human computation for efficient decision input acquisition

When faced with data-intensive decision problems, individuals, businesses, and governmental decision-makers must balance trade-offs between optimality and the high cost of conducting a thorough decision process. The unprecedented availability of information online has created opportunities to make well-informed, near-optimal decisions more efficiently. A key challenge that remains is the difficulty of efficiently gathering the requisite details in a form suitable for making the decision. Human computation and social media have opened new avenues for gathering relevant information or opinions in support of a decision-making process. It is now possible to coordinate paid web workers from online labor markets such as Amazon Mechanical Turk and others in a distributed search party for the needed information. However, the strategies that individuals employ when confronted with too much information--satisficing, information foraging, etc.--are more difficult to apply with a large, distributed group. Consequently, current distributed approaches are inherently wasteful of human time and effort. This dissertation offers a method for coordinating workers to efficiently enter the inputs for spreadsheet decision models. As a basis for developing and understanding the idea, I developed AskSheet, a system that uses decision models represented as spreadsheets. The user provides a spreadsheet model of a decision, the formulas of which are analyzed to calculate the value of information for each of the decision inputs. With that, it is able to prioritize the inputs and make the decision input acquisition process more frugal. In doing so, it trades machine capacity for analyzing the model for a reduction in the cost and burden to the humans providing the needed information

Operation Transforms for a Distributed Shared Spreadsheet

The Distributed Operation Transform (dOPT), proposed by Ellis and Gibbs, is used to define concurrently updatable shared objects. Ellis and Gibbs give the operation transforms that define a simple shared text editor supporting single character insertions and deletions on a linear buffer. We report here on the construction of operation transforms for a more sophisticated groupware application: a shared spreadsheet. We identify a set of abstract operations that characterize the operations on a spreadsheet. Using Cormack's Calculus for Concurrent Update, which extends and corrects dOPT, we give the transforms on these operations necessary to define a shared spreadsheet. We use the transforms to build a shared version of sc, the Unix spreadsheet due to Gosling. KEYWORDS Groupware, Operation Transforms, Distributed Spreadsheets INTRODUCTION We are concerned with asynchronous distributed groupware, in which any copy of a replicated object can be updated at any time, and each update is the..