Some concepts about digital libraries that are encountered in the literature are presented in the paper through preliminary thesaural descriptor structures. Most often coming from different environments on the Web, these new concepts are not clearly discerned and require time for comprehension and acceptance. On the other side, the concepts in question - digital libraries, metadata, Dublin Core metadata, Resource Description Framework, interoperability, portals - are important to modern cooperation projects in the library and information field. Participants of any collaboration venture should commit themselves to a conceptualization and harmonization of the involved conceptual models in order that cooperation be successful. The example of conceptualization has indicated a concept of ontology and his importance for enabling semantics in order to organize and retrieve information in the systems such as the digital libraries.