Christian Fahrner Thomas Marx Stephan Philippi DICE: Declarative Integrity Constraint Embedding Into the Object Database Standard ODMG-93. 119-145 1997 23 Data Knowl. Eng. 2 db/journals/dke/dke23.html#FahrnerMP97 http://dx.doi.org/10.1016/S0169-023X(96)00046-8