Make a relation of a table with three different category of id's table
If I have understood what you need is:

TASK TABLE: ID, NAME, DESCR and other attributes

ROUTING TABLE: *ID, IDTASK, INFO and other attributes**

ANALYSER TABLE: ID, IDROUTING and other attributes

SUBCONTRACTOR TABLE: ID, IDROUTING and other attributes

INTERNE USER TALBE: ID, IDROUTING and other attributes

if you want to trace better the relations, you can add in ROUTING TABLE also 3 foreign key like IDANALYSER, IDSUBCONTRACTOR and IDINTERNEUSER. This is not very efficient, because you will have always 2 values null and only one with a value.

But, you can go straight from ROUTING TABLE to the right detailed table.