Abstract

Abstract. This paper presents a specific approach of integrating a relational database system into a federated database system. The underlying database integration process consist of three steps: first, the external database systems have to be connected to the integrated database system environment and the external data models have to be mapped into a canonical data model. This step is often called syntactic transformation including structural enrichment and leads to component schemas for each external DBMS. Second, the resulting schemas from the first step are used to construct export schemas which are then integrated into global, individual schemas or views in the third step. In this paper we focus on the first step for relational databases, i.e., the connection of a relational database system and the mapping of the relational model into a canonical data model. We take POSTGRES as the relational database system and the object-oriented federated database system VODAK as the integration platform which provides the open, object-oriented data model as the canonical data model lor the integration. We show different variations of mapping the relational model. By exploiting the metaclass concept provided by VML, the modelling language of VODAK. we show how to tailor VML such that the canonical data model meets the requirements of inlegrating POSTGRES into the global database system VODAK in an efficient way.

Efficient evaluation strategies for declarative updates have rarely been investigated. Due to possible dependencies between the resulting database state and the order in which records (objects) are processed, usually declarative updates are evaluated in a set-oriented way in order to ensure a deterministic evaluation. In this paper, we show that such dependencies can be detected by exploiting knowledge about conflicts between the operations that are used to access the database during the update evaluation. Thus most declarative updates can also be evaluated deterministically, and in some cases more efficiently, in a record-oriented way. We show that some of the detected conflicts can be relaxed or even be ignored, while a deterministic evaluation can still be guaranteed.