Measuring OCL expressions: a “tracing”-based approach

Owing that class diagrams constitute the backbone of object-oriented (OO) software development, many metrics were proposed to measure internal quality attributes such as the structural complexity, coupling, size, etc. But none of the proposed metrics take into account the added complexity when class diagrams are complemented by Object Constraint Language (OCL) expressions. OCL expressions improve class diagrams enhancing their semantic properties, adding precision, improving their documentation and understandability. The importance of OCL and the lack of defined metrics for OCL expressions motivate us to propose a set of metrics for structural properties of OCL expressions. The first set of metrics we propose considers only those OCL concepts related to “tracing” technique. We believe that “tracing” technique affects the cognitive complexity, and by consequence the understandability of OCL expressions, and the maintenance of a UML class diagram. Therefore, the main goal of this paper is to show how we defined a set of metrics for structural properties of OCL expressions in a methodological way. We will also present the theoretical validation of these metrics according to a property-based framework proposed by Briand et. al..