The quantity and variety of observations accumulated on about 100000 stars in open clusters are quite impressive and sufficient to motivate the development of a specialised database. Data analysis in open clusters is quite complex and extensive information are often necessary, but are difficult to gather because of the multiple star designations created so far. The star identification problem, already discussed (Mermilliod 1972, 1973, 1976b, 1979a) is not specific to star clusters, but takes on a more accute form. The variety of stars identifications asks for an unavoidable amount of extra work to collect the data available for any star. The necessity to keep on-line track of the cross-references between various numbering systems may be one of the motivations for developing a database.
The database offers one solution to this problem and a coherent data storage and retrieval. The fact that data are kept under a stable format allows to develop tools more easily. It is also a deposit for unpublished data, although the development of anonymous ftp servers has reduced the interest of the database to preserve unpublished data.