To measure the degrees of cohesion, we applied a metric proposed in Oh, Yeom, & Ahn (2011), which measures the cohesion of the modules, i.e. the ontologies, independently of the cohesion of the ontological network. This metric takes into account a factor that ensures the quality of the module. This factor is the degree of internal relations in the module, that is, the degree of cohesion present in the module that undoubtedly influence the coupling with other modules. This also makes it possible to verify the logical consistency between the modules and the complete ontology.
Cohesion in an ontology module has to do with the degree of relationship of the classes in the module. Classes are related when they share properties or have connections with other classes. Therefore, the relations contemplated in this metric can be both hierarchical (the properties of the parent are shared) and non-hierarchical (the classes connect to each other).
Formula 1. Cohesion calculation formula
For this measure, we considered the dependencies established with other modules of the ontology (through import), thar are necessary to complete the defined module.
For every subdomain, we carried out different analysis to obtain:
- Identification of the own classes of the subdomain and identification of possible refinements in the definition of the classes
- Identification of the attributes or data properties of each of the classes
- Identification of the object properties that are resolved within the subdomain that is being modeled
- Definition of cardinalities and obligatory restrictions
- In all cases, we considered the reuse and alignment of ontologies and ontological patterns