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Technical Solutions<br />

Figure 1: Architecture of the SADS system<br />

Due to the potentially huge volume of data that may be retrieved after a user request, it is usually impossible to<br />

provide the answers to the query <strong>in</strong> real time. We thus had to devise other solutions, comb<strong>in</strong><strong>in</strong>g the use of<br />

electronic mail and FTP software, allow<strong>in</strong>g for a more "asynchronous" transfer mode. Accord<strong>in</strong>g to the user's<br />

profile and to the volume of data retrieved by his query, the data may be stored <strong>in</strong> a temporary area of the<br />

SADS, wait<strong>in</strong>g for the user to download it by FTP, or automatically uploaded to the user's site if it is equipped<br />

with a FTP server. It is even conceivable to revert to surface mail for send<strong>in</strong>g the data (which was the usual<br />

transfer mode before SADS), s<strong>in</strong>ce the retrieved volume of data rout<strong>in</strong>ely reaches tens or hundreds of<br />

megabytes. In any case, the user is <strong>in</strong>formed of the availability of his query results by Email.<br />

Introduc<strong>in</strong>g Web Development <strong>in</strong> an Exist<strong>in</strong>g Organization<br />

SADS was conducted <strong>in</strong> the CNES as a prototype project, aimed both at assert<strong>in</strong>g the feasibility of a Web<br />

solution for such a long-term and technically challeng<strong>in</strong>g project, and to explore the Software Eng<strong>in</strong>eer<strong>in</strong>g<br />

problems related to the use of such a new and rapidly evolv<strong>in</strong>g technology.<br />

Most notably, we had to def<strong>in</strong>e how the new programm<strong>in</strong>g techniques and languages related to the HTTP<br />

protocol (HTML, script<strong>in</strong>g languages, public doma<strong>in</strong> tools) could be validated and <strong>in</strong>tegrated <strong>in</strong> the very strict<br />

CNES quality <strong>in</strong>surance plan. This led us to def<strong>in</strong>e development rules and test<strong>in</strong>g techniques for Web<br />

applications, so that the SADS, consist<strong>in</strong>g <strong>in</strong> static HTML pages, dynamically created pages, relational<br />

database model<strong>in</strong>g and programm<strong>in</strong>g and had-hoc gateway software development could be validated with the<br />

same strictness as any conventional software development.<br />

We were also committed to strictly adhere to exist<strong>in</strong>g standards, such as standardization of dates and times <strong>in</strong><br />

compliance with CCSDS recommendations [CCSDS 1990]. We were able to develop a general program for the<br />

extraction of data correspond<strong>in</strong>g to one or more time frames def<strong>in</strong>ed by the user from one or more files. This<br />

program makes it possible to extract only that data which corresponds strictly to the time frame requested by<br />

the user [Fig. 2]. The extraction function is entirely <strong>in</strong>dependent of the archive’s structure:

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