Two of the most significant characteristics of non-functional requirements (NFRs) are "interacting" and "relative". Interacting means NFRs tend to interfere, conflict, and contradict with one other while relative means the interpretation of NFRs may vary depending on many factors, such as the context of the system being developed and the extent of stakeholder involvement. For the purpose of understanding the interacting characteristic of NFRs, several potential conflict models have been presented in the literature. These models represent the positive or negative inter-relationships among various types of NFRs. However, none of them deal with the relative characteristic of NFRs. In fact, multiple interpretations of NFRs in the system being developed may lead to positive or negative inter-relationships that are not always obvious. As a result, the existing potential conflict models remain in disagreement with one other. This paper presents the result of an extensive and systematic investigation of the extant literature over the notion of NFRs and conflicts among them. A catalogue of NFRs conflicts with respect to the NFRs relative characteristic is presented. The relativity of conflicts is characterized by three categories: absolute conflict; relative conflict; and never conflict. This catalogue could assist software developers in identifying the conflicts among NFRs, performing further conflict analysis, and identifying the potential strategies to resolve those conflicts.