  There is considerable amount of sensitive XML data stored in relational
databases. It is a challenge to enforce node level fine-grained authorization
policies for XML data stored in relational databases which typically support
table and column level access control. Moreover, it is common to have
conflicting authorization policies over the hierarchical nested structure of
XML data. There are a couple of XML access control models for relational XML
databases proposed in the literature. However, to our best knowledge, none of
them discussed handling authorization conflicts with conditions in the domain
of relational XML databases. Therefore, we believe that there is a need to
define and incorporate effective fine-grained XML authorization models with
conflict handling mechanisms in the presence of conditions into relational XML
databases. We address this issue in this study.
