This paper proposes a complete DL approach for representing and reasoning on EER (Enhanced Entity-Relationship) models. We develop an equivalence-preserving transformation approach and a prototype tool for transforming an EER model into a DL knowledge base, and propose methods to reduce reasoning on the EER model to reasoning on the transformed DL knowledge base. As one result, the reasoning capabilities of the DL can provide the basic reasoning services that are needed in EER modeling. In detail, we firstly propose a formal definition and semantic interpretation method of EER models, which summarizes and includes all features of EER models. Then , by analyzing the features of EER models, a DL called ALCQIK is presented as the language of representing and reasoning on EER models. On this basis , we propose an approach for transforming EER models into ALCQIK knowledge bases. The correctness of the transformation is proved and a transformation example is provided. Further, a prototype transformation tool is implemented. Case studies show that our approach and prototype tool actually work. Finally , based on the transformed ALCQIK knowledge bases, we propose methods to reduce reasoning on EER models to reasoning on the transformed ALCQIK knowledge bases.