Damien K. Fisher

Algebraic Transformation and Optimization for XQuery

XQuery has been recently proposed by W3C as a standardized query language for XML. Because of its complexity, optimizing XQuery is difficult and requires more complicated optimization schemes than those for traditional query languages. This paper first proposes an XML data model and query algebra to provide a semantics and a means of optimization for the XQuery language. Following the language algebra, algebraic transformation (with optimization rules) is presented. Finally, physical algebraic operators are also defined to specify queries in this algebra into physical query plans.

Efficient ordering for XML data

With the increasing popularity of XML, there arises the need for managing and querying information in this form. Several query languages, such as XQuery, have been proposed which return their results in document order. However, most recent efforts focused on query optimization have disregarded order. This paper presents a simple yet elegant method to maintain document ordering for XML data. Analysis of our method shows that it is indeed efficient and scalable, even for changing data.

Skipping Strategies for Efficient Structural Joins

The structural join is considered a core operation in processing and optimizing XML queries. Recently, various techniques have been proposed for efficiently finding structural relationships between sets of nodes. This paper presents an adaptive algorithm for efficiently processing structural joins. In contrast to previous work, which usually relies on external index structures such as B-trees, our proposal paper does not require any such data structures. Hence, our strategy has lower overheads than previous techniques, and can be easily implemented and incorporated into any existing system. Experiments show that our method significantly outperforms previous algorithms.

Effective clustering schemes for XML databases

Although clustering problems are in general NP-hard, much research effort on this problem has been invested in the areas of object-oriented databases (OODB) and relational databases systems (RDBMS). With the increasing popularity of XML, researchers have been focusing on various XML data management including query processing and optimization. However, the clustering issues for XML data storage have been disregarded in their work. This paper provides a preliminary study on data clustering for optimizing XML databases. Different clustering schemes are compared through a set of extensive experiments.