Official documents, and particularly legal ones like law codes, often contain ambiguities and/or inconsistencies, due to linguistic problems like polysemy, as well as ontological problems like underspecification, disagreements and/or false agreements. Such problems can be identified by formalizing the terminology of a domain in terms of an ontology. We show this phenomenon in a particular domain, the definition of different classes of vehicles. Defining accurately these different vehicle types shed light on some of these semantic deficiencies present in two Brazilian legal codes responsible for defining vehicles’ categories in an unambiguous manner for many purposes, e.g. tax calculations, and, more importantly, to make e-government systems interoperate while taking laws into account in a Semantic Web scenario. In this work, we define a framework linking the linguistic and conceptual problems to semantic deficiencies and show how these deficiencies were identified during the vehicles’ ontology construction.