Papers
Kathi Fisler, Shriram Krishnamurthi, Leo A. Meyerovich, and Michael Carl Tschantz
Verification and Change-Impact Analysis of Access-Control Policies
International Conference on Software Engineering, 2005
Gives an overview of how Margrave version 1 works. See the old website for the example files discussed in this paper.
Michael Matthew Greenberg, Casey Marks, Leo Alexander Meyerovich, and Michael Carl Tschantz
The Soundness and Completeness of Margrave with Respect to a Subset of XACML
Tech Report CS-05-05, Department of Computer Science, Brown University, 2005
A more detailed and theoretical look at the how Margrave version 1 works.
Please note that these papers cover XACML 1.0 and Margrave version 1, not the current version of XACML (version 2.0) or of Margrave (version 2).