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Advanced object-oriented applications require the management of schema versions, in order to cope with changes in the structure of the stored data. Two types of versioning have been separately considered so far: branching and temporal. The former arose in application domains like CAD/CAM and software engineering, where different solutions have been proposed to support design schema versions (consolidated versions). The latter concerns temporal databases, where some works have considered temporal schema versioning to fulfil advanced needs of other typical object-oriented applications like GIS and multimedia. In this work, we propose a general model which integrates the two approaches by supporting both design and temporal schema versions. The model is provided with a complete set of schema change primitives for fully-fledged version manipulation whose semantics is described in the paper.