Towards a metric suite for OCL Expressions expressed within UML/OCL models

UML models quality is clearly a crucial issue that must be evaluated at the initial stages of object-oriented software development, in order to get software products with better quality. This fact is corroborated by the huge amount of metrics that have appeared in the literature related to the measurement of UML diagrams at a high level design stage. Most of these metrics are focused on the measurement of internal quality attributes such as structural complexity, coupling, size, etc. However, none of the proposed metrics take into account the added complexity involved when a UML model are complemented by expressions written in Object Constraint Language (OCL), that is a UML/OCL model. Due OCL is essential in building consistent and coherent platformindependent models we propose a metric suite for structural properties of OCL expressions. These metrics were proposed considering OCL concepts related to the “chunking” and “tracing” cognitive techniques. We believe that cognitive techniques affect the cognitive complexity, and by consequence the understandability and maintainability of expression of UML/OCL models. Therefore, the goal of this paper is to show how we defined these metrics in a methodological way, assuring thus their validity.