Günther Fliedl Christian Kop Willi Mayerthaler Heinrich C. Mayr Christian Winkler Guidelines for NL-Based Requirements Specifications in NIBA. 251-264 2000 conf/nldb/2000 NLDB http://dx.doi.org/10.1007/3-540-45399-7_21 db/conf/nldb/nldb2000.html#FliedlKMMW00