Papers in PDF format

One of the CNES' goals is to make sure that the data gathered during spatial missions can be preserved for
undetermined amounts of time, and that this data remains accessible to a large community of users from the
scientific community. These constraints have led the CNES to conceive and to put in operation a system
allowing these users to identify available data, to select data elements potentially interesting for their research
work, and to access and retrieve this data.
The emerging popularity of the World-Wide-Web and its acceptance as a de-facto standard in the scientific
community have conduced the CNES to base its data access solution on the HTTP protocol and related
technologies such as HTML and CGI gateways, instead of providing a proprietary solution.
Web Access to Huge Amounts of Data
One of the special characteristics of the SADS system is that is aims at offering access to an amazingly huge
amount of scientific data maintained in long term physical storage and conservation service set up by CNES
and known as STAF (Service de Transfert et d'Archivage des Fichiers - file transfer and storage system), which
operates in a heterogeneous environment. This system was conceived and put in operation before the start of the
SADS project, and had to be integrated in our design solution.
Architecture of the SADS System
The SADS is based on the following components [Fig. 1]:
• A metadata management system based on a relational model. This metadata is the data dictionary of the
scientific data that is made available through the SADS. It consists in the description of the data from the
different scientific missions stored in the SADS (e.g. record types and formats) and of some related data that
can be used by the scientists to make queries (e.g. the occurrence of unique events such as solar eruptions or
satellite malfunctions). The metadata is stored in an Oracle database and queried through CGI gateways.
• A physical data storage function compatible with the IEEE mass storage reference model. This is the
purpose of the STAF.
• A metadata access function allowing users to identify available data, to display items available for browsing
and to fill out data queries. The querying may be aided by the visualization of scientific images, which helps the
user in spotting particularly interesting time intervals. A sophisticated user interface allows users to
incrementally construct their queries through thumbnail images browsing and other visual querying techniques.
This is handled by a software package providing also for system protection, data protection and implementation
of generic data extraction mechanisms.
• Data order processing and user delivery functions, which allow registered users to store typical queries
within the SADS, or to automatically transfer query results to their own site.