An Intelligent Search Method for Query Optimization by Semijoins

The problem of finding an optimal semijoin sequence that fully reduces a given tree query is discussed. A method is presented that intelligently navigates the space of all semijoin sequences and returns an optimal solution. Experiments are reported that show that this method performs very efficiently: on average, less than 5% of the search space is searched before an optimal solution is found. Other advantages of the method are ease of implementation, generality of the cost mode considered, and ability to handle tree queries with arbitrary target lists. >