Logical Foundation for Updating XML

With the extensive use of XML in applications over the Web, how to update XML data is becoming an important issue because the role of XML has been expanded beyond traditional applications in which XML is used for data representation and exchange over the Web. Several languages have been proposed for updating XML data, but they have two main drawbacks. One is these updating languages are based on low-level graph-based or tree-based data models so that update requests are thus expressed in a nonintuitive and unnatural way and update statements are too complicated to comprehend. The other is there is still no consensus about the logical foundation for XML updates. This paper presents a declarative language for updating XML data based on a high-level data model and systemically describes its semantics

Effective Schema-Based XML Query Optimization Techniques

Use of path expressions is a common feature in most XML query languages, and many evaluation methods for path expression queries have been proposed recently. However, there are few researches on the issue of optimizing regular path expression queries. In this paper, two kinds of path expression optimization principles are proposed, named path shortening and path complementing, respectively. The path shortening principle reduces the querying cost by shortening the path expressions with the knowledge of XML schema. While the path complementing principle substitutes the user queries with the equivalent lower-cost path expressions. The experimental results show that these two techniques can largely improve the performance of path expression query processing