Abstract

We examine the problem of type evolution in an objectoriented database environment. Type definitions are persistent objects in the database and as such may be modified and shared. The effeets of changing a type extend to objects of the type and to programs that use objeets of the type. We propese a solution to the problem through an extension of the semantic data model. A ehange in the interfaee defined by a type may result in errors when programs use new or old objects of the type. Through the use of an abstraction of the type over time, timestamping and error handling mechanisms provide support for the type designer in creating compatible versions of the type. The mechanisms are incorporated Into the behavior defined by the type and are inherited via the type-lattice. 1.

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