@ARTICLE\{IMM1988-01897,
    author       = "M. R. Hansen",
    title        = "Algebraic Optimization of Recursive Database Queries",
    year         = "1988",
    pages        = "286-298",
    journal      = "INFOR",
    volume       = "26",
    editor       = "",
    number       = "4",
    publisher    = "",
    url          = "http://www2.compute.dtu.dk/pubdb/pubs/1897-full.html"
}