if i pull a model within an iterator in a master model, the oval with the output values isn't vissable like here e. g. http://i.stack.imgur.com/2pCJz.png or http://i.stack.imgur.com/cJ42p.png
I don't find an explanation for this. Have you any idea?
can't load the images on iPad... but if the parameter is supposed to be specified (ie to specify an input or output name) , they need to be specified as a parametr using a P as in these examples
A quick tour of creating tools with ModelBuilder—Help | ArcGIS for Desktop
Is it enough to set <Output Values> (Collect Values) to <Model Parameter> to pass the output of the sub model to the master model?
Yes. A common mistake is to stick say a merge tool on to the end of a workflow which is being driven by an iterator. This is very inefficient as it means the merge tool is running as many times as the iterator. The merge tool needs to run only once as it takes a LIST of inputs. So your Collect Values tool exposed as a parameter is passing out of the sub-model a LIST of featureclasses and it's the master model that has the merge tool in it.
Retrieving data ...