In general, conceptual schemas (CS) are created from scratch, even though several approaches allow the designer to reuse the knowledge included in ontologies. In particular we have defined an approach to create the static CS of an information system (IS) by the refinement of a general ontology. In such a case, a pruning phase is needed in our approach since these ontologies contain too many elements to be usable for humans. The objective of the pruning activity is to remove irrelevant elements from the extended ontology. In this document we describe the algorithms used in the pruning activity and we develop a case study to proof and validate this activity. In this case study we have used the public version of Cyc Ontology as base ontology. For practical reasons we find it convenient to use UML as an ontology language, even though we believe our results apply to any similar language.