I was looking at the amazon website and was wondering how one of the feature would have been implemented. The feature : what customers buy after viewing a particular item.

If i were to develop such a feature i would probably generate a session id for each user session and store the session id-page id combination in a log file. and if a book is bought set a separate flag for the session id-page id. A separate program can then be run on the log file periodically, to identify the groups that were bought together/viewed together and that information can be stored in a persistent file.

This is ofcourse a simple solution without taking into consideration the distributed nature of the servers - but would this suffice or can you help me identify a better design.