This paper presents a survey on the complementarity between databases and ontologies. It interests semantic web and database communities. Ontologies can help in overcoming the drawbacks of DBs and vice-versa. We conducted a deep analysis, which reveals that the collaboration between these two disciplines can be done in five different ways: facilitating the database design, increasing their semantics for information retrieval, integration and maintenance, designing ontologies from existing databases, and allowing storage of large number of instances in ontological systems. We present in this paper the concepts related to this field, the reasons for this rapprochement and a state-of-the-art on existing approaches in this area. For each of the axes presented, we will present the axis, underlying issues and cite relevant research. Originality of our work comes from the fact that it covers the whole field of rapprochement between databases and ontologies. Therefore, it provides the reader, who may not be very familiar with this domain of research, with an introduction to axes in this research and with pointers to different research projects.