Architecture client-server: access modes to databases

This dossier deals with client-server architecture for database (DB) access. DBs are accessed either internally or externally, depending on the type of actor and the data processing to be carried out. The concepts are illustrated by examples using Oracle software and the Java host language. This dossier first presents the types of actors involved in DB access, and then the two main modes of access.

Internal access mainly concerns those responsible for running the database. Four access modes are possible. The characteristics of each mode in terms of data localization, processing and presentation between clients and server are detailed. The centralized approach has the main advantage of minimizing deployment on clients. In contrast, the decentralized approach reduces server congestion. The four modes ("connected" thin client, thick client, "disconnected" thin client, "rich" client) more or less favor one or other of these approaches.

External access is the responsibility of developers of client applications requiring access to databases. These applications are mainly presented using two approaches: thick client and thin client. The first approach offsets as much processing as possible onto the clients, thereby increasing network exchanges between the clients and the data server. Conversely, the second approach places processing on the server, thereby increasing its load.