Use case scenarios are known as powerful means for requirements specification. On the one hand, they join in the same modeling space the expectations of the stakeholders and the needs of the developers involved in the process. On the other hand, they describe the desired high level functionalities. By formalizing these descriptions we are able to extract relevant informations from them. Specifically, we are interested in identifying requirements patterns (common requirements with typical implementation solutions) in support for a requirements based software development approach. This paper addresses the transformation of use case descriptions expressed in a Controller Natural Language into an ontology expressed in the Web Ontology Language (OWL), as well as the query process for such information. It reports on a study aimed at validating our approach and our tool with real users. A preliminary set of results is discussed.