We propose a DBMS the data model of which is an extension of the Entity-Relationship model of Chen. The main extensions include the specialization and generalization concepts of Smith & Smith and the possibility to define relationships between relationships. In addition we extend the concept of a role in a relationship, to a multi-valued role which enables to associate a set of tuples performing the same function in a relationship. A query language has been designed in order to deal with the enhanced semantic capabilities of the data model supported by the ECRINS/86 system.