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://link.springer.de/link/service/series/0558/bibs/1959/19590251.htm db/conf/nldb/nldb2000.html#FliedlKMMW00