OCL support in EA

[Stephanie]

I would like to use OCL to improve my meta models. However there is only very little information about it in the help.
I played around a bit but made no progress.

I would like to express very simple things like:

In my meta model I would like to add constraints for required attributes, so that when I use this stereotype in my models this constraint is then applied to the referring tagged values.

I tried the following for my stereotype:

inv: self.attrName <> ''

But it threw an ocl viaolation for all model elements the stereotype was applied to.

Is there anyone around that uses OCL in EA freuwently and can give me some hints , samples how to use OCL in the right way in meta modells?