Facilities offered by the database

The database offers several working facilities and some are described below. Three examples are discussed by Mermilliod (1992b).

• Data comparaison: Data comparaison is an important step before starting any study. Tools have been developed to compare data coming from different sources. This concerns essentially the UBV system because the UBV data represents a large fraction of the published photometric data. The other photometric systems seldom present two or more different sources of data.

• Colour-magnitude diagram manipulation: The main tool of the database allows to plot the various diagrams that can be built in the UBV and Geneva photometric systems. It offers a large spectrum of facilities, like fitting sequences or computing isochrones. Extensions have to be developed for other photometric systems (uvby, Walraven and others).

• Technical data: The technical information on instruments and data acquisition systems may also prove important to characterise the data contained in the database. Pioneering work has been done by van Leeuwen (1985) who collected the information on telescopes and plates related to proper motion studies in open clusters. This information is available in the database. The collection of similar information on telescopes and spectrographs used for radial velocity determination has been started. It would also be necessary to collect the same information for CCD photometry.

• Miscellanous facilities: To avoid remembering many commands and their options, a number of menus have been written which group most actions concerning a given subject. Those built up so far are generally related to the maintenance and development of the database, and were especially designed to facilitate the introduction of new data. In this category, one finds:
  1. the management of coordinates: it was made to determine coordinates of stars in open clusters starting from (x,y) positions in arbitrary units and include them in the database;
  2. the management of rectangular position: (x,y) positions are now often published with CCD data. In addition many published charts have been measured and the results included in the database;
  3. the management of cross-references: to maintain the principles of the database, it is necessary to determine the cross-references between any new numbering system and those already existing.