Data sharing is a critical factor for the success of organizations due to the increasing need to facilitate communication with business partners. However, data source heterogeneity proved to be a barrier for the effective interoperability between information systems. The concept of an Ontology- based Object Catalog (OnOC) is first introduced as a strategy to address the interoperability problem between heterogeneous data sources. An OnOC offers support for the definition and maintenance of a common vocabulary, called a reference ontology, that facilitates data interchange among different sources. Then, an architecture for OnOCs is proposed that combines concepts such as metadata catalogs, ontology servers, mediators and database federations.