Before revision: OpenSees (the Open System for Earthquake Engineering Simulation) is a proprietary object-oriented , software framework created at the National Science Foundation-sponsored Pacific Earthquake Engineering (PEER) Center.
After revision: OpenSees (the Open System for Earthquake Engineering Simulation) is an object-oriented , software framework creduringera (1997-2007) of theResearched at the National Science Foundation-sponsored Pacific Earthquake Engineering (PEER) Center.