Efficient query evaluation in XML information subscription systems

In this paper, we propose two methods of improving the efficiency of query evaluation in XML information subscription systems, where the users register queries to the server, and they are evaluated periodically. First, we show a method of optimizing communication costs between client sites and the server sites. In information subscription systems, when a user registers many queries, the answers to those queries can be redundant. Therefore, sending those redundant answers separately to the client is not optimal. In our approach, the server sends a minimal-size view set that can answer all the original queries, and the client produces answers from it. We show algorithms for computing a minimal view set for given queries. Second, we show a method of improving the efficiency of query evaluation on the servers. In information subscription systems, registered queries are evaluated periodically, and only changes to the answers to those queries are not fled to the users. We show a method of incrementally computing only changes to the answers to the given queries upon the updates of the database.