Nikos A. Lorentzos Yannis Manolopoulos Functional Requirements for Historical and Interval Extensions to the Relational Model. 59-86 1995 17 Data Knowl. Eng. 1 db/journals/dke/dke17.html#LorentzosM95 http://dx.doi.org/10.1016/0169-023X(95)00026-O