Using cognitive techniques for assessing the influence of coupling on the maintainability of OCL expressions

This paper is part of a project we have been developing for the past three years, related to the maintainability of expressions written with the Object Constraint language (OCL). Our objective is to find which elements of OCL influence on the comprehensibility and modifiability of OCL expressions. Coupling is recognized as a key characteristic of software artifacts, which affects comprehensibility and maintainability. In addition, whenever an expression operates in a large context, modelers need to know all the UML artifacts the expression relies on. Therefore, we believe that coupling should also affect to the comprehension of OCL expressions and, consequently, their modifiability. We believe that two main factors of the import coupling are the number of different objects which are coupled to the contextual instance and the depth of coupling. For measuring these factors we have defined two measures (the number of navigated classes -NNC- and the depth of navigation -DN-) based on two cognitive techniques (chunking and tracing). For testing if both coupling measures (and their interaction) could be indicators of the comprehensibility and modifiability of OCL expressions, we carried out a specific family of experiments which will be carefully described in this paper. The obtained results confirm our hypothesis, revealing that coupling really affects to the maintainability of OCL expressions.