Like any other database application object database applications are subject to
evolution. Evolution is, however, critical in object databases because it is the very
characteristic of complex applications such as CAD, etc. for which they provide inherent support. This paper discusses the evolution facilities offered by some of the existing systems. We first provide an overview of the ODMG 2.0 standard from an evolution viewpoint. We then describe our extension to the database evolution features specified by the ODMG 2.0 standard. Using this extension as a basis we form evaluation criteria, which we employ to assess the various evolution facilities offered by four commercially available object database management systems: POET, Versant, O2 and Jasmine.