Non Functional Requirements (NFRs) are relative, so are the conflicts among them. In our previously developed catalogue of NFRs conflicts it can be observed that a number of specific pairs of NFRs are claimed to be in conflicts in some cases but they are also claimed not to be in conflict in the other cases. These relative conflicts occur because the positive or negative relationships among NFRs are not always clear and obvious. These relationships might change depending on the meaning of NFRs within the system being developed. This paper focuses on the application of ontology in managing the relative conflicts among NFRs, particularly the relative conflicts between security and usability requirements. The aim is to develop a framework to identify, characterize, and define corresponding resolution strategies for the security-usability conflicts. This paper thus describes the sureCM framework to manage these conflicts; summarizes the security-usability conflicts ontology; and demonstrates how the ontology will be used as a basis to assist analysts in managing conflicts between security and usability requirements.