@Article {bbfs.tods98,
    author = {E. Bertino and C. Bettini and E. Ferrari and P. Samarati},
    title = {An Access Control Model Supporting Periodicity Constraints and Temporal Reasoning},
    journal = {ACM Transactions on Database Systems (TODS)},
    volume = {23},
    number = {3},
    pages = {231-285},
    month = {September},
    year = {1998}
}