The main difficulty in enforcing global serializability in a multidatabase environment lies in resolving indirect (transitive) conflicts between multidatabase transactions. Indirect conflicts introduced by local transactions are difficult to resolve because the the behavior or even the existence of local transactions is not known to the multidatabase system. To overcome these problems, we propose to incorporate additional data manipulationoperations in the subtransactions of each multidatabase transaction. We show that if these operations create direct conflicts between subtransactions at each participating local database system, indirect conflicts can be resolved even if the multidatabase system is not aware of their existence. Based on this approach we introduce a multidatabase transaction management method that requires the local database systems to ensure only local serializability. The proposed method and its refinements do not violate the autonomy of the local database systems an...

To enforce global serializability in a multidatabase environment themultidatabase transaction manager must take into account the indirect (transitive) conflicts between multidatabase transactions caused by local transactions. Such conflicts are difficult to resolve because the behavior or even the existence of local transactions is not known to the multidatabase system. To overcome these difficulties, we propose to incorporate additional data manipulation operations in the subtransactions of each multidatabase transaction. We show that if these operations create direct conflicts between subtransactions at each participating local database system, indirect conflicts can be resolved even if the multidatabase system is not aware of their existence. Based on this approach, we introduce optimistic and conservative multidatabase transaction management methods that require the local database systems to assure only local serializability. The proposed methods do not violate the autonomy of the local database systems and guarantee global serializability by preventing multidatabase transactions from being serialized in different ways at the participating database systems. Refinements of these methods are also proposed for multidatabase environments where the participating database systems allow schedules that are cascadeless or transactions have analogous execution and serialization orders. In particular, we show that forced local conflicts can be eliminated in rigorous local systems, local cascadelessness simplifies the design of a global scheduler and that local strictness offers no significant advantages over cascadelessness.

. Database applications often impose temporal dependencies between transactions that must be satisfied to preserve data consistency. The extant correctness criteria used to schedule the execution of concurrent transactions are either time independent or use strict, difficult to satisfy real-time constraints. On one end of the spectrum, serializability completely ignores time. On the other end, deadline scheduling approaches consider the outcome of each transaction execution correct only if the transaction meets its real-time deadline. In this paper, we explore new correctness criteria and scheduling methods that capture temporal transaction dependencies and belong to the broad area between these two extreme approaches. We introduce the concepts of succession dependency and chronological dependency and define correctness criteria under which temporal dependencies between transactions are preserved even if the dependent transactions execute concurrently. We also propose a chronological s...

To support global transactions in a multidatabase environment, we must coordinate the activities of multiple Database Management Systems, that were designed for independent, stand-alone operation. The autonomy and heterogeneity of these systems present a major impediment to the direct adaptation of transaction management mechanisms developed for distributed database systems. In this paper we address the problems in multidatabase recovery. We show that most solutions proposed to provide multidatabase recovery are either allow incorrect results or place severe restrictions on global and local transactions. To assure that multidatabase recovery preserves the consistency of a multidatabase system, we introduce a multidatabase recoverability requirement. We also describe a recovery mechanism that takes advantage of the local recovery in the participating database systems by minimizing the replication of recovery tasks. 1 Introduction A Multidatabase System (MDBS) [15] is a facility that ...

Distributed database technology is expected to have a significant impact on data processing in the upcoming years. With the introduction of commercial products, expectations are that distributed database management systems will by and large replace centralized ones within the next decade. In this paper, we reflect on the promises of distributed database technology, take stock of where we are, and discuss the issues that remain to be solved. We also present new research issues, such as distributed object-oriented systems, distributed knowledge bases, multiprocessor data servers, and distributed multidatabase systems, that arise with the introduction of new technology and the subsequent relaxation of some of the assumptions underlying current systems. Keywords: distributed database, data distribution, transaction management, distributed query procesing, object-oriented system, knowledge base, multidatabase system. * An abridged version of this paper has appeared as "Distributed Databas...

Distributed heterogeneous databases consist of systems which differ physically and logically, containing different data models and data manipulation languages. Although these databases are independently created and administered they must cooperate and interoperate. Users need to access and manipulate data from several databases and applications may require data from a wide variety of independent databases. Therefore, a new system architecture is required to manipulate and manage distinct and multiple databases, in a transparent way, while preserving their autonomy. This report contains an extensive survey on heterogeneous databases, analysing and comparing the different aspects, concepts and approaches related to the topic. It introduces an architecture to support interoperability among heterogeneous database systems. The architecture avoids the use of a centralised structure to assist in the different phases of the interoperability process. It aims to support scalability, an...

PEER is a federated object management system developed at the University of Amsterdam. In this paper, the design of the prototype implementation architecture of PEER is described. This implementation is based on an object-oriented database model and language. PEER is mainly intended to represent and support the complex data interrelation and information exchange in multi-agent industrial automation applications. Such applications usually form decentralized networks of agent clusters, where some agents are tightly and some loosely interconnected. To support data consistency, applications mostly desire that the information is not redundantly stored. Agents are heterogeneous in their design, in modeling their information, and in the information they store, and they are autonomous in sharing a part of their information with other agents in the network community. An innovative approach taken in the design of PEER federated architecture is the support for the definition, manipula...

Information Integration is a young and exciting field with enormous research and commercial significance in the new world of the Information Society. It stands at the crossroad of Databases and Artificial Intelligence requiring novel techniques that bring together different methods from these fields. Information from disparate heterogeneous sources often with no a-priori common schema needs to be synthesized in a flexible, transparent and intelligent way in order to respond to the demands of a query thus enabling a more informed decision by the user or application program. The field although relatively young has already found many practical applications particularly for integrating information over the World Wide Web. This paper gives a brief introduction of the field highlighting some of the main current and future research issues and application areas. It attempts to evaluate the current and potential role of Computational Logic in this and suggests some of the problems where logic-based techniques could be used. 1

In this paper a knowledge base structure to support multiple view generation over a federation of loosely-coupled heterogeneous databases available over a computer network is described. In such a federation user information requirements change and evolve as their awareness of the contents of the federation improves. This means that users need different integrating views if they are to realise the full potential of the federation. To facilitate the creation of integrating views, users need to know what is available in the federation, how the available information is related semantically and which information has been used together previously. Once integrating views are created, users must be informed when their views become invalid due to changes in the participating databases. The knowledge base is structured primarily to assist users in such tasks. The knowledge stored in the knowledge base is obtained by analysing the meta-data of the databases of the federation and from their respec...

The research reported in this thesis is concerned with supporting interoperability among sets of pre-existing and heterogeneous object-oriented databases without forcing them to conform to a common data model, query language and DBMS, i.e. these databases preserve their local autonomy. Special attention has been paid to logically heterogeneous object-oriented databases - where heterogeneity arises through independent design. We have focussed on supporting multiple integration views over the participating databases - as different users have different reasons for integration and the same user may need to integrate the same set of local integration units in various ways to suit different roles or tasks. Thus this research avoids the rigidity of a one-toone correspondence between merging rules and local integration units, and allows local conflicts to be reconciled in various ways according to user requirements and preferences. To this end, we have designed a schema integration language ca...