@Article {bfs.tapos98,
    author = {E. Bertino and E. Ferrari and P. Samarati},
    title = {Mandatory Security and Object-Oriented Systems: A Multilevel Entity Model and its Mapping onto a Single-Level Object Model},
    journal = {TAPOS - Journal on Theory And Practice of Object Systems},
    volume = {4},
    number = {3},
    pages = {183-204},
    year = {1998}
}