Query Translation for XPath-Based Security Views

Since XML is used as a storage format in an increasing number of applications, security has become an important issue in XML databases. One aspect of security is restricting access to data by certain users. This can, for example, be achieved by means of access rules or XML security views, which define projections over XML documents. The usage of security views avoids information leakage that may occur when we use certain access rules. XML views can be implemented by materialized views, but materialization and maintenance of views may cause considerable overhead. Therefore, we study translations from queries on views to equivalent queries on the original XML documents, assuming both the security views and the queries are specified by XPath expressions. Especially, we investigate which XPath fragments are closed under the composition of a view and a query.