The file may be an Objectivity Database file, or a Zebra FZ file. We thus prefer to execute queries close to the data, depending on the tradeoff between available processing power and this transfer latency. In the system, end-users will be issuing selection queries about the available data. How the query is formulated, and how it gets parsed, is defined and controlled by the analysis tool being used. This will be made possible by the development of middleware into which the chosen analysis tool is inserted.
Agents are small entities that carry code, data and rules in the network.
They move on an itinerary between Agent servers that are located in the system. The Primary site, all the Regional centres and the Department systems run Agent servers. For each query, an Agent is created in the most proximate Agent server in the Test Bed system, on behalf of the user. The Agent intercepts the query, generates from it a set of required data files, decides where the query should execute, and then despatches the query accordingly. Clearly, it needs to take into account the speed of the media on which the file is stored, its latency and so on.