6 Conclusion

The usage of the CDS services has undergone a revolution in the last few years, with the outcome of the World Wide Web, allowing easy access to on-line information, the integration of data and documentation, and navigation between distributed information. This means an explosion in the usage of the services, new functionalities, new concepts in the partnership of data centers and journals, since published information can now be considered as data (e.g., published tables are now usable like reference catalogues), and an increase in international partnership, to build up links and to define exchange standards. In parallel, the construction of the database contents remains a long-term activity, with increasing volume of information to deal with, and high standards of scientific and technical expertise needed in the value-added data center activities.

Navigation and links will certainly remain important keywords for the future, and the topic of interoperability is clearly emerging. One aspect is the construction of links between distributed services. Another one is the building of comprehensive information retrieval tools, as stressed in the AstroBrowse NASA initiative. To go further, one needs to be able to integrate the result of queries to heterogeneous services (ISAIA project, Hanisch [2000]). In this context, the elaboration of exchange standards and metadata descriptions common to all service providers are fundamental keys to success. On a technical point of view, XML may be one important tool for data integration. ALADIN is an example of a comprehensive tool, allowing integration of reference images, with information from catalogues, databases and data archives.

The rapid development of the world-wide "bibliographic network'' has been particularly impressive, and the "data archive network'' seems well under way. The CDS is a major hub in the on-line "Virtual Observatory'' presently under construction: its services allow astronomers to select the information of interest for their research, and to access original data, observatory archives and results published in journals.

Acknowledgements

CDS acknowledges the support of INSU-CNRS, the Centre National d'Études Spatiales (CNES), and Université Louis Pasteur. Many of the current developments have been made possible by long-term support from NASA, ESA and ESO, and Astronomy & Astrophysics. Many other partners are involved in building up the international astronomy network, among which are the AAS, ADS, HEASARC, IPAC and NED, STScI, ADC, CADC, INASAN, NOAJ, and many others which cannot all be cited here.

Developing and maintaining the data-bases is a collective undertaking. The expertise and dedicated work of the documentalists, engineers and astronomers who work for CDS in Strasbourg and elsewhere are the foundations of the quality of the services. All of them are associated with this paper. Long term support from Institut d'Astrophysique de Paris, Observatoire de Paris (DASGAL), Observatoire de Bordeaux, GRAAL (Montpellier) and Observatoire Midi-Pyrénées (Toulouse), is gratefully acknowledged.

We thank Jean Delhaye, Jean Jung, Carlos Jaschek, and Michel Crézé, for their vision and leadership in the different phases of the CDS project.