Norbert Kiesel Andy Schürr Bernhard Westfechtel GRAS, a Graph-Oriented (Software) Engineering Database System. 21-51 1995 20 Inf. Syst. 1 db/journals/is/is20.html#KieselSW95 http://dx.doi.org/10.1016/0306-4379(95)00002-L