Abstract: A method is provided for selecting a query execution plan, including: receiving an XML document including a plurality of root nodes and a plurality of leaf nodes; determining root-to-leaf paths based on the plurality of root nodes and the plurality of leaf nodes; generating a prime number for each unique root-to-leaf path; calculating a number of instances in which each prime number appears; generating an XML synopsis based on the prime numbers and the number of instances; determining a comparison between a query tree pattern and the XML synopsis; determining a type of the query tree pattern; calculating for each query tree pattern plan, a selectivity estimate based on the comparison and the type of the query tree pattern; determining an optimal query execution plan based on the selectivity estimate; and selecting the optimal query execution plan for performing a query of the XML document based on the determination.

Abstract: The hierarchal clustering method for large XML data is a scalable technique that takes large XML data sets and measures distances between those sets of data and then arranges those data into groups according to the distance measurements. The method can cluster XML data by both content and structure, and can cluster homogeneous XML data.