ObjectGen is a tool for generating test objectives from use cases. ValueGen is a tool for generating operational variables and combination of values from use cases. Although ValueGen needs the artefacts generated by ObjectGen, both tools are independent.
M. Friske, and H. Schlingloff. Tagungsband Dagstuhl-Workshop MBEES: Model Based Engineering of Embedded Systems III, 2005-01, TU Braunschweig, (January 2007)