2 Access modes

After a long phase of development, (see e.g., Paillou et al. [1994]), ALADIN has been first distributed to a limited number of astronomy laboratories in 1997, as an X-Window client program, to be installed on a Unix machine on the user side. The client program interacts with the servers running on Unix workstations at CDS (image server, catalogue server, SIMBAD server) and manages image handling and plane overlays.

The strategy of having a client program on the user side is difficult to maintain on the long run. The World-Wide Web offers, with the development of Java applications (or applets), a way to solve this difficulty. Actually, there is still a client program: this is the Java applet itself, that the user receives from the WWW server. Most current Internet browsers are able to make it run properly, so that the user does not have to install anything special other than an Internet browser.

As a consequence, ALADIN is currently available in the three following modes:

ALADIN previewer:

a pre-formatted image server provides a compressed image of fixed size ( $14.1\hbox{$^\prime$ }\times 14.1\hbox{$^\prime$ }$ for the DSS-I) around a given object or position. When an object name is given, its position is resolved through the SIMBAD name resolver. Anchors pointing to the previewer are integral part of the World-Wide Web interfaces to the SIMBAD database and to the CDS bibliographic service. The result page also gives access to the full resolution FITS image for download.

ALADIN Java:

this is the primary public interface, supporting queries to the image database and overlays from any catalogue or table available at CDS, as well as from SIMBAD and NED databases. Access to personal files is not possible (due to security restrictions of the Java language). These restrictions do not apply to the stand-alone version, which can be installed and run on a local Java virtual machine.

ALADIN X:

The X-Window ALADIN client provides most of the functionalities of the ALADIN Java interface, plus more advanced functions, as described below (Sect. 6).