An extensible view system for supporting the integration and interoperation of heterogeneous, autonomous, and distributed database management systems

In this thesis the problem of integrating heterogeneous, autonomous and distributed database management systems (DBMSs) is addressed. To provide a solution, we have developed an approach, a design method, and a view system. Our approach is based on the invention of the abstract view constructs that have uniform and stable representations for supporting semantic relativism and distributed abstraction modeling. Our design method applies object-oriented techniques and software engineering concepts to manage the system complexity. Our view system has been constructed upon established experience with the development of large-scale distributed systems in a distributed object infrastructure provided by the Common Object Request Broker Architecture (CORBA). The scope of our research identifies the goals of Project Zeus in which we have created the Zeus View Mechanism ( ZVM) as the theoretical foundation of our approach. The notion of frameworks has been introduced as part of our design methodology to promote code/design reuse and enhance the portability/extensibility of the architectural design. A multidatabase system, the Zeus Multidatabase System ( ZMS), has provided a test bed for our concept. Project Zeus has exciting prospects. The foundation established in this research has created new directions in multidatabase research and will have a significant impact on future integration and interoperation technologies

Adaptable Mobile Transactions and Environment Awareness

National audienceMobile environments are characterized by high variability (e.g. variable bandwidth, disconnections, different communication prices) as well as by limited mobile host resources. Such characteristics lead to high rates of transaction failures and unpredictable execution costs. This paper introduces an Adaptable Mobile Transaction model (AMT) that allows defining transactions with several execution alternatives associated to a particular context. The principal goal is to adapt transaction execution to context variations. An analytical study shows that using AMTs increases commit probabilities and that it is possible to choose the way transactions will be executed according to their costs. In addition, the middleware TransMobi is proposed. It manages environment awareness and implements the AMT model with suitable protocols.Les environnements mobiles sont caractérisés par une grande variabilité (bande passante variable, déconnexions, prix de communication différents, etc.) ainsi que par des uni-tés mobiles à ressources limitées. Ces caractéristiques entraînent un nombre important de défaillances transactionnels et des coûts d'exécution imprévus. Cet article introduit un modèle de transactions mobiles adaptables (AMT) permettant de définir des transactions avec plusieurs alternatives d'exécution. Le principal objectif est d'adapter l'exécution des transactions aux variations du contexte. Une étude analytique montre que les AMT augmentent la probabilité de validation et qu'il est possible de choisir le type d'exécution en fonction de son coût. Nous proposons également l'intergiciel TransMobi gérant la perception de l'environnement et implantant le modèle AMT à l'aide de protocoles appropriés

Global Semantic Integrity Constraint Checking for a System of Databases

In today’s emerging information systems, it is natural to have data distributed across multiple sites. We define a System of Databases (SyDb) as a collection of autonomous and heterogeneous databases. R-SyDb (System of Relational Databases) is a restricted form of SyDb, referring to a collection of relational databases, which are independent. Similarly, X-SyDb (System of XML Databases) refers to a collection of XML databases. Global integrity constraints ensure integrity and consistency of data spanning multiple databases. In this dissertation, we present (i) Constraint Checker, a general framework of a mobile agent based approach for checking global constraints on R-SyDb, and (ii) XConstraint Checker, a general framework for checking global XML constraints on X-SyDb. Furthermore, we formalize multiple efficient algorithms for varying semantic integrity constraints involving both arithmetic and aggregate predicates. The algorithms take as input an update statement, list of all global semantic integrity constraints with arithmetic predicates or aggregate predicates and outputs sub-constraints to be executed on remote sites. The algorithms are efficient since (i) constraint check is carried out at compile time, i.e. before executing update statement; hence we save time and resources by avoiding rollbacks, and (ii) the implementation exploits parallelism. We have also implemented a prototype of systems and algorithms for both R-SyDb and X-SyDb. We also present performance evaluations of the system

Transactional Agents for Pervasive Computing

Pervasive computing enables seamless integration of computing technology into everyday life to make upto- date information and services proactively available to the users based on their needs and behaviors. We aim to develop a transaction management scheme as a pertinent component for such environment supported by either structured or ad hoc networks. We propose Transactional Agents for Pervasive COmputing (TAPCO), which utilizes a dynamic hierarchical meta data structure that captures the semantic contents of the underlying heterogeneous data sources. Mobile agents process the transactions collaboratively, to preserve ACID properties without violating local autonomy of the data sources. TAPCO is simulated and compared against Decentralized Serialization Graph Testing (DSGT) protocol. The results show that TAPCO outperforms DSGT in several ways. In contrast to DSGT that did not consider local transactions, TAPCO supports both local and global transactions without violating the local autonomy

CORBA: a middleware for an heterogeneous cooperative system

Two kinds of heterogeneities interfere with the integration of different information sources, those in systems and those in semantics. They generate different problems and require different solutions. This paper tries to separate them by proposing the usage of a distinct tool for each one (i.e. CORBA and BLOOM respectively), and analizing how they could collaborate. CORBA offers lots of ways to deal with distributed objects and their potential needs, while BLOOM takes care of the semantic heterogeneities. Therefore, it seems promising to handle the system heterogeneities by wrapping the components of the BLOOM execution architecture into CORBA objects.Postprint (published version

The mediated data integration (MeDInt) : An approach to the integration of database and legacy systems

The information required for decision making by executives in organizations is normally scattered across disparate data sources including databases and legacy systems. To gain a competitive advantage, it is extremely important for executives to be able to obtain one unique view of information in an accurate and timely manner. To do this, it is necessary to interoperate multiple data sources, which differ structurally and semantically. Particular problems occur when applying traditional integration approaches, for example, the global schema needs to be recreated when the component schema has been modified. This research investigates the following heterogeneities between heterogeneous data sources: Data Model Heterogeneities, Schematic Heterogeneities and Semantic Heterogeneities. The problems of existing integration approaches are reviewed and solved by introducing and designing a new integration approach to logically interoperate heterogeneous data sources and to resolve three previously classified heterogeneities. The research attempts to reduce the complexity of the integration process by maximising the degree of automation. Mediation and wrapping techniques are employed in this research. The Mediated Data Integration (MeDint) architecture has been introduced to integrate heterogeneous data sources. Three major elements, the MeDint Mediator, wrappers, and the Mediated Data Model (MDM) play important roles in the integration of heterogeneous data sources. The MeDint Mediator acts as an intermediate layer transforming queries to sub-queries, resolving conflicts, and consolidating conflict-resolved results. Wrappers serve as translators between the MeDint Mediator and data sources. Both the mediator and wrappers arc well-supported by MDM, a semantically-rich data model which can describe or represent heterogeneous data schematically and semantically. Some organisational information systems have been tested and evaluated using the MeDint architecture. The results have addressed all the research questions regarding the interoperability of heterogeneous data sources. In addition, the results also confirm that the Me Dint architecture is able to provide integration that is transparent to users and that the schema evolution does not affect the integration