Database Description

The database purpose

The database tries to collect all published data for stars in open clusters that may be useful either to determine the star membership, or to study the stellar content and properties of the clusters.

It has been developed not only to be an efficient tool to store and retrieve data, but also to provide a versatile environment to analyse the data and study open clusters considered as interesting astrophysical objects worth a systematic study.

The database history

The database for stars in galactic open clusters, known as BDA has been developed since 1987 at the Institute for Astronomy (University of Lausanne, Switzerland) by the author. The extensive collections of observational data cover most significant domains and concerns about 200000 stars in some 500 NGC, IC and anonymous clusters.

The first database (BDA) used compressed flat ASCII files to store the data. It has been decided in 1996 to migrate to the /rdb database system, which offers a number of interesting facilities, in connection with the development of a public access.

The database contents

The database contents includes measurements in most photometric systems in which cluster stars have been observed, spectroscopic observations, astrometric data, various kinds of useful information, and extensive bibliography.

The data are usually recorded in their original form, with an indication of the source, but also as averaged values or selected data when relevant. The mean values for UBV (photoelectric, photographic or CCD) are not kept in the database, but can readily be computed.

The greatest effort has been spent in solving the identification problems raised by the definition of so many different numbering systems and a special interface has been developed to query the cross-reference tables.

Maps for about 200 clusters have been scanned and included in the database.

The database structure

The database structure uses the directory hierarchy supported by the Unix system. The main directory is the database itself. It contains several sub-directories: description of the database, help information, references, bibliography, programs, perl scripts.

Each cluster defines an independent directory identified by its name and containing the available data in distinct files, one for each data type. This structure allows easy inclusion of any new cluster and any additional data type.

Whenever possible, the records of the various data files have the same structure: star identification, source, data. The files are organised sequentially and, within the files, the entries are sorted by star number and source reference. Due to the small size of many files, there is no need for indexing, but it could be done within /rdb.

The star identification is the main key to access the data, but it is also possible to use filters based on the bibliographic references or astrophysical parameters.

The present database structure is thought of as a first step in the organisation of cluster data and bibliography. When enough data analysis has been performed and only one set of data for each type will be available for each star, it may be perhaps more convenient to adopt another structure and collect all the data in one file for each cluster.

The database engine

WEBDA is a relational database built upon the package /rdb developed by Rod Manis, Evan Schaffer and Robert Jorgensen.

/rdb is a high performance relational database management and application development system designed for Unix and implemented as a suite of 131 shell level commands. It is an extension of the Unix environment.

Database utilities, such as sorttable, jointable, row, column and compute are programs invoked by the shell which read tables from the standard input and write tables to the standard output.

All relational operators are included, as well as several indexing methods, a vi-like forms editor, a powerful report generator and menus.

See the /rdb home page for further information.

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Last update: 12 November 1999