Arda Goknil Ivan Kurtev Klaas van den Berg A Metamodeling Approach for Reasoning about Requirements. 310-325 2008 ECMDA-FA http://dx.doi.org/10.1007/978-3-540-69100-6_21 conf/ecmdafa/2008 db/conf/ecmdafa/ecmdafa2008.html#GoknilKB08