Along the requirements elicitation process, communication problems appear between analysts and stakeholders; usually, these problems cause losing of functional requirements. Refinement of conceptual schemas-particularly class diagram-lessens the impact of these losses. Some approaches to the refinement of class diagram have been proposed, but they do not evidence cycles of interaction with the stakeholder; other approaches show interactive refinement of the Entity-Relationship diagram, which does not have all the information contained in class diagram. In this paper, we propose the refinement of UML class diagram through interaction with stakeholders. To achieve this goal, we propose completeness rules in natural language and the use of a corpus of class diagrams for complementing the analyst knowledge in a specific domain. Finally, we illustrate completeness analysis with a prototype in the UNC-Diagrammer tool and we propose a case study.