A Semantic Approach to Correctness, of Concurrent Transaction Executions (Classic Reprint)

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Excerpt from A Semantic Approach to Correctness, of Concurrent Transaction Executions One of the main Issues in concurrency control is the question of what constitutes a legal or correct behavior of a group of transactions updating the database simultaneously. It seems that the undesirable effects of concurrent transaction executions can be put into three classes: violation of integrity constraints, inconsistent outputs to users and racing. An intuitive way to define correctness of transaction schedules is then to require that the scheduler avoid all three types of anomalies. In this paper, we formalize this notion of correctness. To do this, we develop a new, desirable, semantic property of transaction schedules, which we call independence. Then, we give a partial answer to the following question: Is there any intermediate class of schedules, between the classes of serializable and correct schedules, that has an easy membership test? We first prove a negative result. For integrity constraints in the form of linear inequalities and for linear semantics of transaction actions, we show that the serializable schedules are the only class of schedules preserving those integrity constraints. However, if the semantics of transaction actions are more restricted, then there exists a class of nonserializable schedules (we call them weakly serializable of order 2) which is a proper subset of the class of correct schedules and has an easy membership test. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully, any imperfections that remain are intentionally left to preserve the state of such historical works.