Hippocratic XML databases: a model and an access control mechanism

Abstract

The Hippocratic database model recently proposed by Agrawal et al. incorporates privacy protection capabilities into relational databases. Since the Hippocratic database is based on the relational database, it needs extensions to be adapted for XML databases. In this paper, we propose the Hippocratic XML database model, an extension of the Hippocratic database model for XML databases and present an efficient access control mechanism under this model. In contrast to relational data, XML data have tree-like hierarchies. Thus, in order to manage these hierarchies of XML data, we extend and formally define concepts presented in the Hippocratic database model. Next, we present a new mechanism, which we call the authorization index, that is used in the access control mechanism. This authorization index, which is implemented using a multi-dimensional index, allows us to efficiently search authorizations implied by the authorization granted on the nearest ancestor using the nearest neighbor search technique. Using synthetic and real data, we have performed extensive experiments comparing query processing time with those of existing access control mechanisms. The results show that the proposed access control mechanism improves the wall clock time by up to 14 times over the top-down access control strategy and by up to 20 times over the bottom-up access control strategy. The major contributions of our paper are (1) extending the Hippocratic database model into the Hippocratic XML database model and (2) proposing an efficient access control mechanism that uses the authorization index and nearest neighbor search technique under this model.