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Introduction to Database Reverse Engineering

Jean-Luc Hainaut, May, 2002, 140 pages, English [full text]

This text is an extended abstract for a future book devoted to database reverse engineering (DBRE), considered as a specific, but general purpose, activity of information system engineering, and particularly system reengineering. To give it as large a scope as possible, we have developed general principles that can easily be specialized for any actual data management system, ranging from simple file managers (COBOL or RPG) to modern DB managers such as relational systems and OO DBMS. These principles are organized as a general DBRE methodology that is built in a systematic way. This methodology can be specialized according to specific DBMS models. It can be used to compare methodologies proposed in the literature and through reverse engineering CASE tools.

Contents. 1. Introduction. 2. Data schema specification. 3. Database development revisited. 4. A general database reverse engineering methodology. 5. The data structure extraction process. 6. The data structure conceptualization process. 7. DMS-oriented DBRE methodologies. 8. CASE technology for DBRE. 9. A case study: Database Migration. 10. State of the art and conclusion. 11. References.

Integration of Legacy and Heterogeneous Databases

Philippe Thiran, Jean-Luc Hainaut, 2002, 204 pages, English [full text]

Accessing and managing data from several existing independent databases pose complex problems that can be classified into platform, DMS, location and semantic levels. The platform level copes with the fact that databases reside on different brands of hardware, under different operating systems, and interacting through various network protocols. Leveling these differences leads to platform independence. DMS level independence allows programmers to ignore the technical details of data implementation in a definite family of models. It can also hide the model that the DMS implements by providing a more abstract model. Location independence isolates the user from knowing where the data reside. Finally, semantic level independence solves the problem of multiple, replicated and conflicting representations of similar facts.The InterDB project proposes a general architecture, a methodology and a CASE environment intended to address the problem of providing users and programmers with an abstract interface to independent, heterogeneous and distributed databases.

Architecture. The architecture comprises a hierarchy of mediators that dynamically transform actual data into a virtual homogeneous database. Each layer of mediators provides a certain kind of independence. DMS independence is provided by wrappers dedicated to each database. Location and semantic independence’s are ensured by a mediator. Finally, platform independence is ensured by both the wrappers and ad hoc middleware such as commercial ORB.

Methodology. Such an architecture involves controlling complex mappings. The problem is complicated by the fact that the databases have been developed independently, and naturally suffer from sever problems of replication and semantic conflicts. In addition, most legacy databases have no documentation any more, just like programs. Recovering the conceptual schemas form an existing database is the main goal of database reverse engineering, an important software engineering that can now be considered mature. Solving the syntactic and semantic conflicts of independent schemas has long been studied in the database realm. However, coping with conceptual schemas form populated databases brings new problems. A complete methodology, encompassing conceptual schema recovery and database integration is provided to practitioners.

Case support. Deriving a common, abstract and conflict-free image of independent databases and defining the mappings between the specification layers are complex tasks. Building the wrappers and the mediators are also two complex and error-prone activities. All these processes are supported by the DB-MAIN CASE tool. This graphical, repository-based, software engineering environment includes, among others, a sophisticated reverse engineering toolkit, schema mapping specification facilities and a generator development environment.

Contents.

1 Introduction

Part I: Generic Integration Framework. 2. Integration Architecture. 3. Generic Data Model. 4. Mapping Definition.

Part II: Wrapper Technology. 5. Wrapper Architecture. 6. Wrapper Development (Methodology). 7. Wrapper Development Support.

Part III: Mediator Technology. 8. Mediator Architecture. 9. Mediator Development (Methodology). 10. Meditator Development Support.

References.

Introduction pratique aux bases de données temporelles

Jean-Luc Hainaut, Virginie detienne, novembre 2002, 116 pages, français [full text]

Présentation et discussion, au travers d'une étude de cas construite pas à pas, des principes des bases de données temporelles. On étudie la représentation de la dimension temporelle des données (monotemporel physique et logique, le bitemporel est simplement évoqué), la gestion de données temporelle sous la forme d'une base de données active en SQL2 and l'exploitation de données temporelle (y compris la projection, la jointure et l'agrégation temporelles).

Presentation and discussion, through a case study developed step-by-step, of the basics in temporal databases. The tutorial studies the temporal dimension of data (transaction time and valid time are developed but bitemporal is just mentioned), the management of temporal data through an SQL2 active database and its exploitation (including temporal projection, join and agregation).

Contenu. 1. Introduction. 2. Description du projet. 3. Représentation des données historiques. 4. Gestion des données historiques (temps physique ou transaction time). 5. Gestion des données historiques (temps logique ou valid time). 6. Interrogation d’une base de données historiques. 7. Projection temporelle d’une table historique (version simplifiée). 8. Projection temporelle généralisée. 9. Jointure de tables historiques. 10. L’agrégation temporelle. 11. Normalisation d’une table historique. 12. Variantes d’historiques. 13. Historique d’associations. 14. Suggestions d’extension. 15. PROJET : Les composants du projet. 16. PROJET : Les structures de données. 17. PROJET : La gestion des données. 18. PROJET : Quelques applications représentatives. 19. Bibliographie.

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