This paper presents the design and implementation of lhe O•Raid system which has been developed by extending an existing distribuLed. database system called Raid. The system design encom• passes lhe simplicity of the relational model, Ute extensibility of lite objcct-orienled model, and the inLen1ctive aspects of language-oricnLed edilors. The resulting system has several novel properties. Objects, classes, and inheritance are supported together with a predicate-based relational query language. A hierarchy of colwnn protocols define !.he common properties of objects in a particular relation column. Relations may contain heterogeneous objects that can individually evolve by being reclassified. Special facilities are provided to reduce the data search in a relation containing complex objects. A sbUcLureediting interface integrated with me query language allows me editing of complex objects. A special query suppons continuous display of objects in me database. 'This research is supponcd by NASA and AIRMICS under granL number NAG-l~76. and UNISYS.