@Article {bds.tissec02,
author = {P. Bonatti and S. {De Capitani di Vimercati} and P. Samarati},
title = {An Algebra for Composing Access Control Policies},
journal = {ACM Transactions on Information and System Security (TISSEC)},
volume = {5},
number = {1},
pages = {1-35},
month = {February},
year = {2002}
}