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Introduction

All data obtained at the telescopes of the Observatório do Pico dos Diaz (OPD) of the Laboratório Nacional de Astrofísica (LNA) are stored on backup tapes which are kept at the observatory. These tapes constitute de facto a data bank. In order to become useful, information about the contents of these observations and their availability must be disseminated. It is the purpose of DaBIAS (Data Bank Information Acquisition System) to keep a complete record of the observations, to put this information onto the internet, to provide means for the potential user of the databank to search on-line for observations of particular objects or at particular locations at the sky, to request data, and thus to permit a feedback between the scientific community and the data bank.

The heart of DaBIAS is a UNIX shell script which is also called DaBIAS [For easier distinction, hereafter DaBIAS (written in normal font) will stand for the entire software system, while DaBIAS (written in typewrite font) means the UNIX shell script.] However, other shell scripts and programs are also part of the system. In order to minimize the work load for the data bank manager and to guarantee a stable long-term performance of the system it is imperative that the process to make the desired information available to the public is completely automatic. Thus, the final version of the shell script will be started automatically each morning after the observing night in order to update the available information which is then put on the Internet to make it public. The current version v2.0 has not yet quite achieved this stage: The script DaBIAS is started manually after the observations of each night have been transformed from IRAF-format to FITS-format according to the normal observatory operations.

For the time being DaBIAS will only be applied to the observations obtained with the various CCD-cameras (and the IR camera) of the OPD (be it direct cameras or cameras attached to spectrographs), operated by the routine OPDPIX under the IRAF environment. This restriction is implemented in order to deal only with a homogeneous set of data formats. Data acquisition systems for e.g. the FOTRAP or the FOTEX are quite different and would constitute serious complications, requiring a structure of DaBIAS very different from that suitable for the instruments run under OPDPIX. To which extent data from those instruments can be incorporated later into the data bank remains to be defined.

The general structure of the DaBIAS system is outlined schematically in Fig. 1.

The general structure of DaBIAS

The observed data of each night are stored on disk at the OPD. Since they were obtained in the IRAF environment they are available as data files in IRAF-format. These data are transformed into FITS-files and stored on backup EXABYTE tapes by the staff of the OPD. This happens during the day following the observing night (or during the first working day in case of weekends or holidays). Of course, the observer also takes a copy of the data home. Due to the limited capacity of the hard disks, data of at most a few nights are kept on disk. Thereafter, they are deleted. Before the data are removed from the hard disk - normally immediately after the observing night - the DaBIAS shell script is started and performs a series of tasks which ultimately result in the generation of files which are put on the Internet in order to make the information about the observed objects available to the general public. DaBIAS is mainly concerned with an analysis of the headers of the data files.

Version v2.0 only works on files in FITS-format. IRAF-formats are not considered. This is due to the fact that the one of the most important bits of information for the data bank, the name of the observed object, which is available under the keyword OBJECT in FITS-files, is not a keyword in the header of IRAF-files but is coded in some other (and different for different implementations of IRAF) way. This -- together this the fact that IRAF cannot be started in a mode where input commands are read from a command file instead of the console which makes it impossible for the DaBIAS script to transform the data files automatically from IRAF-format to FITS-format - is the principle reason why in the current implementation DaBIAS is not started automatically each morning but has to await the manual transformation of formats before it is started by the operations crew of the OPD. It is planned to overcome this difficulty in the next version of DaBIAS.

The DaBIAS script:

The WWW pages

The HTML pages created on a daily basis by DaBIAS are put on the WWW server of the LNA. The structure of the corresponding Web-site is shown schematically in Fig. 2.

The following description of the structure of the data bank web-site reflects the current status. Since it is in continuous development, differences may be introduced at any time! It is an experimental phase and political decisions concerning the data bank which might have bearings on its structure are still pending. Moreover, no particular attention has been payed to the layout of the web pages. For the time being they are kept very simple. As times goes by a more appealing layout may be developed.

The data bank web pages (including those which are created on-line by CGI-scripts) are layered in 6 levels, each of which provides more specific information about the available data. In detail, contents of the individual levels are as follows:

  1. The first level consists of the Welcome page of the data bank. It contains some brief information concerning the data bank and links to the pages on the next level.
  2. The second level contains:
  3. The third level contains pages listing the dates for which data are available in the data bank. A kind of calendar is provided with those days for which data are available constituting links to the corresponding NS files. In order not to permit these lists to grow ad infinitum over the years, only the dates of the current year are listed. Links to corresponding pages for previous years are also provided. There are separate pages of this kind for each telescope.
  4. The pages on level four finally get to the data. These are the NS files mentioned previously. For each day for which data are available, a summary is given, containing: The graphs of the metereological conditions during the night available in future at this level will show the variations of the following quantities at a time resolution of 30 minutes from the noon preceding the observing night until the moment at which the DaBIAS script is started (or until noon of the day following the observing night if DaBIAS is only run on a later day): In a later version of DaBIAS it is planned to get this information together with information about the seeing (for the 1.6-m telescope; to be taken from the autoguider which is currently under construction) for each individual observation (to be included into the data file header).
  5. On level 5, a page for each of the objects observed during the night is provided. It lists the most important items of each exposure of the corresponding object:
  6. Finally, level 6 contains a page for each individual exposure. Here the contents of all header keywords are listed (with the exception of a few keywords which are not relevant to judge the usefulness of the data such as e.g. BSCALE or BZERO).
Of course, this structure of the data bank web site must not be regarded as static. It will certainly develop as experience with the performance of the data bank is being gained.

Data retrieval

For the time being, it is not expected that the number of requested data will be very large. Therefore, it is not yet planned to automatize the response to a data request by a user. Several ways to comply with a user request are possible. Presently, two of these are considered viable within the current approach for the data bank. They are not exclusive; and both of them can be followed, depending on the amount of requested data. In order to keep the work load of the data bank manager within limits, he will not bother with too detailed a user request: Instead of copying individual data files to the FTP Server or the tape, all of a night's (and telescope's) data are made available to the user. It is then up to him to down-load (or read from tape) only those files which he is interested in, discarding the rest.