The previous section pointed out commonsense reasoning as a means to support systems capability to react to unexpected situations. However, before getting into the details about how these tasks are performed, we set the basis for the knowledge representation task, prior to tackling the reasoning one. This knowledge engineering task (Brachman et al., 2004) can be summarized so as to identify the relevant entities, their properties and their relationships one to each other, or in other words, providing an ontology for the application domain.