A metamodel definition presents some important issues in the construction of an object database management system, whose rich data model inevitably increases the metamodel complexity. The required features of an object database metamodel are investigated. Roles of a metamodel in an objectoriented database management system are presented and compared to the proposal defined in the ODMG standard of object-oriented database management systems. After outlining the metamodel definition included in the standard, its main drawbacks are identified and several changes to the ODMG metamodel definition are suggested. The biggest conceptual change concerns flattening the metamodel to reduce complexity and to support extendibility.

Advanced object-oriented applications require the management of schema versions, in order to cope with changes in the structure of the stored data. Two types of versioning have been separately considered so far: branching and temporal. The former arose in application domains like CAD/CAM and software engineering, where different solutions have been proposed to support design schema versions (consolidated versions). The latter concerns temporal databases, where some works considered temporal schema versioning to fulfil advanced needs of other typical objectoriented applications like GIS and the multimedia ones. In this work, we propose a general model which integrates the two approaches by supporting both design and temporal schema versions. The model is provided with a complete set of schema change primitives for full-fledged version manipulation whose semantics is described in the paper. Keywords: Schema versioning, Schema evolution, OODBMS, Temporal databases 1 Introduction In th...

The evolution of information systems from their conceptual schemas is an important research area in information systems engineering. In this paper, we aim at contributing to the area by focusing on a particular conceptual modeling construct, the partitions.

A database metamodel is inherent to every DBMS. Appropriate constructs reflect the declarations of data-definition and data-manipulation languages, and are necessary to implement the internal DBMS mechanisms. Particularly, a metamodel definition provides a base for implementation of database's schema repository. However in object-oriented DBMS these notions are often treated implicitly or (as in case of ODMG standard) suffer from rather ad-hoc approach to their definition. This work is intended to show the importance of providing an explicit database metamodel definition that is both simple and extensible. The main roles of database metamodel have been enumerated. Since different responsibilities of database metamodel together with inherent complexity of object data model can easily lead to unacceptably complicated metamodel definition, the radically simplified, "flattened" form of metamodel structure is proposed. Moreover, the proposed solution assumes the usage of generic means to manipulate database metadata instead of a large set of narrowly specialize operations assumed by the ODMG standard. The prototype implementation of metadata repository is provided to prove the feasibility of the simplified metadata structure. To show the importance of metamodel extensibility, the database schema-based mechanism to support the configuration management of ODBMS application has been implemented over the flattened metamodel structure. A number of additional remarks, concerning future extensions to a database metamodel as well as its capability to accept custom extensions in the context of current challenges for database management systems, have been presented.