The NL-OOPS project started in 1994 as a joint project between the Computer and Management Science Department of Trento University (I) and the Laboratory for Natural Language Engineering, Department of Computer Science, of Durham University (UK). NL-OOPS, acronym for Natural Language - Object-Oriented Production System, is a tool that supports requirements analysis by generating object-oriented models from natural language requirements documents. Our goal was to develop a system capable of generating OO models analysing natural language requirements. As we do not assume that the language used by the analysts and users has to be a subset of NL, it is necessary to use a ‘real’ NL processing system, able to tackle a full range of NL problems (e.g., the quantification problem).