The IFC data model has several hundred entities and thousands of attributes, relationships, quantity and property sets that can represent various aspects of a construction project. A one-to-one mapping between a BIM software tool's native data format and the IFC data exchange standard is not possible. This complexity makes it difficult for the translator modules in a BIM software tool to accurately map the IFC elements, causing interoperability problems while exchanging BIM data using IFC. Also, there are mistakes made by the software developers in implementing the mapping to and from IFC data exchange standard, which adds to the issue. A proposed approach to tackle the interoperability problem is to adopt a 'divide and conquer' method by classifying IFC entities as per their relative importance for a discipline and to rectify the interoperability issues of the most important entities first. This paper proposes a framework to classify the IFC entities as per their relative importance with respect to various disciplines and introduce an index called RI (Relative Importance). This paper also suggests the application of the proposed framework in the interoperability measurement (conformance testing) implementation for BIM software tools, and in presenting the results of conformance tests.