This paper presents the Kuaba Ontology, a knowledge representation model for Design Rationale described in an ontology definition language. The representation of this model in a specific ontologies specification language, such as OWL or F-Logic, allows attributing semantics to recorded Design Rationale content, and defining rules that enable performing computable operations to support the use of Design Rationale in the design process of new artifacts. In addition, we propose to support the software design process through the use of the semantic descriptions defined by formal models of the artifacts. Representing Design Rationale using an ontology definition language and the artifacts formal model, enables a type of software reuse at the highest abstraction level, where rationales are re-employed in designing a new artifact. This kind of reuse is possible in knowledge domains where there are formal models describing the artifacts, in particular, in the Software Design domain.