Design and Software Development

After a preliminary study (1992/1993) and the installation of a local prototype (1993), the project has now started its development phase.

The architecture is based on the client-server philosophy which, optimizes access to distributed computing resources and offers modularity and flexibility, thus making much easier further hardware and software evolutions of the system.

ALADIN is composed of 5 main pieces of software : a graphical user interface, the CDS multimedia server, the Image database server, the Catalogue server and the SIMBAD server.

Communications between the user interface and the CDS server, and between servers and databases, are designed according to the client/server model.

The access to the system from the outside world is managed by the ``CDS multimedia server'' which is connected to each dedicated server through the CDS local network.

The SIMBAD server:

The SIMBAD software was not originally (1988) written following this client/server approach: a server mode has been recently added to the ``user interface class" (Bonnarel et al. 1994). In order to make easier the development of new user interfaces to the database, a set of client routines has been developed on top of the communication layer of SIMBAD. These routines allow to retrieve objects on the basis of identifiers or coordinates, and to extract the corresponding data (defined by simple ``astrotypes") and the full bibliographical references.

The Catalogue server:

The CDS maintains since 1972 an archive of astronomical catalogs in machine-readable form, currently yielding a collection of over 650 catalogs. The requests issued by ALADIN for extraction of data from the astronomical catalogs are essentially based on the following two criteria: choice of the catalogs to be scanned, according to a predefined purpose (e.g. catalogs for photometric calibration, with IR data, etc.), and region of the sky to be examined.

The Image Database

is currently under development. Its main function is to retrieve sets of images according to astronomical criteria: survey, color, region of the sky, etc. The selection of the images is made using Image Qualifiers stored in a relational database. In order to give a great modularity to each step of the request, an object oriented design has been retained for the software. Image Set, Image Qualifier, Image Archive and Image are the basic classes of the software.

The CDS multimedia server

is the common gateway to all the databases and archives of the CDS. An object oriented design has also been retained for this software.

The User Interface

is an X-Window/Motif distributed client, providing Image Display functionalities and various menus for querying the CDS databases and archives and displaying the data and images.

Astronomical packages, such as astrometric and photometric calibration tools, source extraction, classification, will also be provided.