The paper deals with the design of an intelligent interface aimed at assisting end-users in accessing a large and complex technical data base (namely, the European Reliability Data System - ERDS) in a friendly, correct, and effective way. The interface includes both natural language understanding and expert problem solving capabilities and features a modular architecture devoted to cope with the exigencies of both technical and non-technical users. In the paper a brief introduction to ERDS is first presented and the problems related to its use are analysed. The requirements of the users of ERDS are then investigated, and the basic architecture of an intelligent interface is illustrated. The design criteria of the two main modules of the interface, namely the natural language query interface and the expert interface, are later discussed. At last, the present state of the project is reported and promising directions for future research are outlined.