The database started with the installation of the data already collected and kept on magnetic tapes. Several catalogues had been announced and made available through the Strasbourg Data Center: UBV photometry and MK spectral types in open clusters (Mermilliod 1976a, 1986a), UBV photographic data (Mermilliod 1984a), individual radial velocities (Mermillliod 1979b, 1984b), cross-reference tables (Mermilliod 1979a), cross-identifications with astronomical catalogues (Mermilliod 1986b). Unpublished compilations made by me and containing CCD data, rotational velocities, membership probabilities and positions were used at the first installation of the database.
Aditional photoelectric photometric data were taken from the compilations made in our institute, and among them data in the following systems: uvby (Hauck &Mermilliod 1985), DDO (Mermilliod &Nitschelm 1989), Walraven (Nitschelm &Mermilliod 1990).
The files remained on magnetic tapes until the installation of Unix workstations and large disks in our institute made it possible to keep the data on-line. The data were organised in a database designed in March 1987 (Mermilliod 1988a, 1988b) and the compilations of cluster data were discontinued in their older form. New published data are entered regularly. A progress report on the introduction of recent data has been published in the CDS Bulletin (Mermilliod 1992a).
The bibliography from Alter et al. (1970) and the information from Lyngå's (1987) catalogue were taken from the files distributed by the Strasbourg Data Center.