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Principles of organization

The ideology of CATS is shortly described in (Trushkin et al., 1996, Verkhodanov et al., 1997). Here we show some details.

We constructed our database in the UNIX operating system without involving any standard data base systems because of three main reasons:
(a) they are very expensive commercial products;
(b) there are no human resources to develope them in ob--
servatory now;
(c) our task is simplier to solve it with complex systems (however, we do not exclude a probability to use such systems in future).

Therefore, we have designed our data base using simple principles, permitting us to include easily new information to our data base system (see Fig. 1):

  1. every new catalog of objects has to be contained in the UNIX directory having the same name as the catalog of objects;
  2. the description of the catalog must also be in that directory;
  3. the programs for local operations (programs of low level) with the catalog of objects are also in the same directory;
  4. brief characteristics and names of the programs and file with the description of the catalog are stored in the file cats_descr;
  5. there are scripts (programs of high level) operating with every low level program and documentaion of each catalog, and accessable from the UNIX standard shells, graphics and WWW system.
Thus, we can consider a unification of the UNIX directory, the catalog of astrohysical data, programs to operate with them, and description as a unit (object) of our data base. And the problem is to organize the best and fast operation of such objects.

The catalog description file ( cats_descr) contains the name and type of the catalog (radio, optical, mixed, etc.), frequency range, minimum fluxes or magnitudes, type of coordinates (equatorial or/and galactic), names of the local programs for the select and match functions (both designed in "C" programming language), name of the document file, number of records in the catalog, resolution, calibration factor for obtaining the common scale of flux densities, and the reference.

To simplify the disign of CATS operating programs, two utilites of 'select' and 'match' type have been worked out. These utilites operate with the pattern string, describing a format of the ASCII table with astrophysical data.

A user operates with CATS from any directory since the programs for general use of the catalogs are accessible system-wide.

The described manner of catalog storage eases the database development, its expansion with new data and the fine-tuning of the supporting programs.

All astronomical catalogs have a different format and list different observables. It will be a major challenge to provide uniform access to such a heterogeneous collection of data sets based on different methods, using different notations and units (in the absence of a ``standard'' to create catalogs). Except for parameter-dependent derived quantities, we intend to use all different fields (i.e. columns of data tables) as they were published.

The concept of a ``Reference Directory'' (a central repository of metadata like the descriptions of fields for each catalog, their physical units, mapping of original field names to the actual name in the database, etc), would be extremely important to unify the ``look'' of the catalogs as well as to process user queries.

CATS is capable to accomplish the following tasks:

  1. Provide a short description and characteristics of each catalog; print the full list of catalogs relevant for a given sky area.
  2. Select objects from one or several catalogs matching user-specified criteria, like equatorial and galactic coordinates, flux densities and spectral indices, observing frequency, names of catalogs unified in mixed catalogs and object type (if provided by the catalog).
  3. Cross--identification of different catalogs and selection after calculation of spectral indices.
  4. Drawing radio spectra of selected sources in the PostScript language, GIF-format or JAVA language.

The result of the object selection can be sent to the standard output or saved in the following formats:

  1. The original format of the input catalog.
  2. A standard format, common for all catalogs and used further for unification and operation with spectra or other parameters. The standard FITS TABLE header describing the various data fields of the table may be recorded with the resulting file.
  3. X-window codes or tape archives (TAR format) of compressed PostScript files for graphical spectra of radio sources.

The result of the CATS operation is an 'ASCII'-file sorted according to different object characteristics. It can be used for subsequent investigation of the radio source spectra or statistical source properties in the RATAN--600 data processing system (Verkhodanov et al., 1993).

next up previous
Next: Format of data Up: Further advance in the Previous: Introduction

Vladimir Chernenkov
Tue Jun 17 12:02:11 MSD 1997