Hi Dojo
I have a device with 5 codecs. Each with some settings that are displayed in a table. I want to have the unit name in the display key in all of these tables, so a foreign key is needed to the connections table. Since they all share the same primary key i wondered if that could be used as a primary key.
I tried it out and defined a relation between the security table and the connections table, with the primary key of the security table as foreign key and defined the naming format to use the unit name of the connections table to build the display key. This seems to work, DIS doesn't flag it as an issue bit the table editor does. What are the guidelines on this? 
Hi Arne,
As DIS shows you in the Table Editor, PKs should not be used as FKs.
Instead, It would be best to create a duplicate column for each foreign key you want to define.
Given that the entire table is retrieved you can add an extra column with the duplicate value or if this were a different kind of table like SNMP you could also use concatenation type.
You can read more about the best practices at the bottom of this Docs page Foreign keys | DataMiner Docs.
Hi Arne
The documentation (at the bottom) also mentions to not specify the FK on the index as this could not work: Foreign keys | DataMiner Docs
Even though it works for you now, won't mean that it will continue to work. This is currently undefined behavior and is not supported.