I browsed some of the threads about queries, but what I am trying to do seems so simple that there should be a simple way to do it... The object Control has several properties like the Org-Unit that implements it (one or many), the risks it controls (again, one or many), etc. I would like to have create query that listed all the Controls and for each control the Org-Units that implement it and the Risks it controls.
In MEGA a query returns a list of object names
To do what you want, you need to browse objects and this cannot be done using a simple query
Control --> Org-unit (probably using the MetaAssociationEnd 'Responsible (Org-unit)')
Control --> Riks (probably using the MetaAssociationEnd 'Controlled Risk')
What you need is a report. There are several technologies of reporting.
A common one is RTF Descriptors
See the user manual MEGA Publisher EN.pdf, section, Customizing RTF descriptors
As jerome mentions, the rft descriptors are a good way to do this. The result is than a word document.
Another solution might be a script in MEGA that puts the result in excel, this gives you also the possiblity afterwards to apply filters in excel, sorting, etc.
There are also the analysis reports in MEGA which might be a good way to go.