@unpublished{TUW-180681, author = {B{\"o}hm, Johannes and Van Dam, Tonie}, title = {Position Paper 'Modeling Deficiencies and Modeling based on External Data'}, year = {2009}, note = {invited; talk: GGOS Unified Analysis Workshop, San Francisco, USA; 2009-12-11 -- 2009-12-12} }