Recently, the demand for data integration on the Geological domain has increased. Most approaches for database schema integration are strongly based on structure and syntax, and present limitations. Semantic resources, such as ontologies, have been used to reach better results for data integration. However, these approaches assume there are already local ontologies that represent the databases involved in the interoperation. Furthermore, the creation of an ontology based on the database logical schema is not an easy task. On the other hand, it had been proposed that the association of a top-level ontology to a database conceptual schema may lead to better interoperability results. The idea is to make explicit the ontological commitment of each representation, and thus facilitate their integration. This work presents a case study on the Geological domain, which aimed at making explicit the ontological commitment of a database conceptual schema, in order to further improve data interoperability. The main contribution of this work is that it covers the whole process. It starts from the database logical schema, applies a set of reverse engineering techniques to create a preliminary database conceptual schema, and then uses a top-level ontology as a way of making explicit its ontological commitment. A detailed description is provided on how each step was taken, serving as a roadmap for others that may need to go through a similar process on the geological domain or on other domains.