Dolors Costal Cristina Gómez Anna Queralt Ernest Teniente Drawing Preconditions of Operation Contracts from Conceptual Schemas. 266-280 2008 CAiSE http://dx.doi.org/10.1007/978-3-540-69534-9_22 conf/caise/2008 db/conf/caise/caise2008.html#CostalGQT08