However sometimes you want to automate tests with for example soapUI. In this case it is advised to generate a webservice from the Decision Table. This is nicely described here.
However I ran into a problem that the prefix of namespaces must be entered when the Decision Table was selected.
After a while I found the problem.
You use Schema files for the input of a Decision Table. Go to the definition of the Schema and double click it:
The you should check the Namespace Prefix in this namespace. This prefix must NOT be empy.
When I filled in the prefix I was able to generate the webservice on the Decision Table again.