Recently, extensions for relatlonal database management systems (DBMS) have been proposed to support also herarch& structures (complex objects) These extensions have been mamly unplemented on top of an exlstmg DBMS Such an approach leads to many dlsadvantages not only from the conceptual pomt of view but also from performance aspects Thus paper reports on a 3-year effort to design and prototype a DBMS to support a generahzed relatlonal data model, called extended NFZ (Non Fist Normal Form) data model which treats flat relations, hyts, and hlerarctical structures m a umform way The log& data model, a language for thts model, and altematlves for storage structures to unplement generabzed relations are presented and discussed
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