Flow diagram of TheoSSA. The VO user sends an SED request to the GAVO database by entering the photospheric parameters. If a suitable model is available within the desired tolerance limits, it is offered as a results table. In case that the parameters are not exactly matched, the VO user may decide to calculate a model with the exact parameters. TMAW will start a model-atmosphere calculation at our institute’s (IAAT) PC cluster then. Extended model grids make use of computer resources that are provided by AstroGrid-D. As soon as the model is converged, the VO user can retrieve the SED table from the GAVO database.