On Securely Manipulating XML Data

Over the past years several works have proposed access control models for XML data where only read-access rights over non-recursive DTDs are considered. A small number of works have studied the access rights for updates. In this paper, we present a general and expressive model for specifying access control on XML data in the presence of the update operations of W3C XQuery Update Facility. Our approach for enforcing such update specification is based on the notion of

query rewriting

. A major issue is that, in practice, query rewriting for recursive DTDs is still an open problem. We show that this limitation can be avoided using only the expressive power of the standard XPath, and we propose a linear algorithm to rewrite each update operation defined over an arbitrary DTDs (recursive or not) into a safe one in order to be evaluated only over the XML data which can be updated by the user. To our knowledge, this work is the first effort for securely updating XML in the presence of arbitrary DTDs, a rich class of update operations, and a significant fragment of XPath.