7 Integration of distributed services

While the CDS databases have followed different development paths, the need to build a transparent access to the whole set of CDS services has become more and more obvious with the easy navigation permitted by hypertext tools. ALADIN has become the prototype of such a development, by giving comprehensive simultaneous access to SIMBAD, the VIZIER Catalogue service, and to external databases such as NED, using a client/server approach and, when possible, standardized query syntax and formats.

In order to be able to go further, the CDS has built a general data exchange model, taking into account all types of information available at the Data Center, known under the acronym of GLU for Générateur de Liens Uniformes - Uniform Link Generator (Fernique et al. [1998]).

More generally, with the development of the Internet, and with an increasing number of on-line astronomical services giving access to data or information, it has become critical to develop new tools providing access to distributed services. This is, for instance, the concern expressed by NASA through the AstroBrowse project (Heikkila et al. [1999]). A local implementation of this concept is available at CDS (AstroGlu: Egret et al. [1998]).