Diagram-based UML notation is limited in its expressiveness thus producing a model that would be severely underspecified. The flaws in the limitation of the UML diagrams are solved by specifying UML/OCL combined models, OCL being an essential add-on to the UML diagrams. Aware of the importance of building precise models, the main goal of this paper is to carefully describe a family of experiments we have undertaken to ascertain whether any relationship exists between object coupling (defined through metrics related to navigations and collection operations) and two maintainability sub-characteristics: understandability and modifiability of OCL expressions. If such a relationship exists, we will have found early indicators of the understandability and modifiability of OCL expressions. Even though the results obtained show empirical evidence that such a relationship exists, they must be considered as preliminaries. Further validation is needed to be performed to strengthen the conclusions and external validity.