XML access control: from XACML to annotated schemas

XML became the de facto standard for the data representation and exchange on the internet. Regarding XML documents access control policy definition, OASIS ratified the XACML standard. It is a declarative language allowing the specification of authorizations as rules. Furthermore, it is common to formally represent XML documents as labeled trees and to handle secure requests through “user views”. A user view is the part of the document accessible to a given user according to the existing policy. Moreover, control access polices can be depicted as annotated rules where annotations define for each document node whether it is accessible. Hence, an annotated schema is a formal representation of “user views”. Our main contribution in this paper is then three folds. First, we compare XACML policies and annotated schemas. Second, we identify a significant fragment of XACML since this latter is very expressive and consequently complex. Third, we define adequate translation algorithms from XACML policies to annotated schemas.