Schema conversion approaches convert images of complex objects. The schema conversion is performed on images of complex objects belonging to a root class, whether those objects are instances of the root class or instances of a subclass of the root class. A complex object is an object that is comprised of a collection of objects or that has another object as an attribute. The approaches use change vectors to represent changes to make to an image to convert it between the target schema version and source schema version. Change vectors are generated based on schema version records, each of which describes the properties of a schema version, including the attributes in the schema version and the data type of each of the attributes. The approaches evolve changes that includes addition, modification and deletion of object attributes. They convert from an earlier schema version to a later schema version, and vice versa, i.e. from a later schema version to a earlier schema version.