In this paper, we have benefited from having an object algebra maintaining closure that makes it possible to have the output from a query persistent in the hierarchy. Based on this, it is possible to maximize reusability in object-oriented databases. Furthermore, we show how the object algebra is utilized to handle basic schema evolution functions without requiring any special set of built-in functions to serve the purpose. The invariants and the conflict resolving rules are specified. It is also shown how other schema functions are derivable from the basic ones.