@MISC\{IMM2004-03535,
    author       = "M. R. Hansen",
    title        = "Duration Calculus",
    year         = "2004",
    pages        = "364-385",
    publisher    = "",
    address      = "",
    url          = "http://www2.compute.dtu.dk/pubdb/pubs/3535-full.html"
}