The Effect of Coupling on Understanding and Modifying OCL Expressions: An Experimental Analysis

Not all the model constraints can be defined using only UML graphical features due to the limited expressiveness of diagram-based UML notation. To solve this problem, the OCL language was defined as a textual add-on to the UML diagrams, allowing the specification of a wide range of constraints of objects. Aware of the lack of metrics to capture the quality aspects of UML/OCL models and the importance of models in recent initiatives of model-Driven software engineering (such as Model-Driven Development and Model-Driven Architecture), we define a set of metrics for measuring the structural properties of OCL constraints in UML/OCL models. Many of these metrics are defined in terms of navigations, a core concept of OCL that defines coupling between objects. This paper carefully describes a family of experiments we have conducted to ascertain whether any relationship exists between object coupling (defined through metrics related to navigations and collection operations) and two maintainability subcharacteristics: understandability and modifiability of OCL expressions. Empirical evidence that such a relationship exists is shown in the obtained results, however they must be considered as preliminaries results. Further validation is needed to strengthen the conclusions and external validity.