Make a relation of a table with three different category of id's table I have an issue 
There a table that's called "Routing" this table is for routing a task for three category of object 
      - 


Analyser (interne machine)
      - 
subcontractor (externe )
Manually (interne worker)


how to design a relation between 5 tables 

   1 - task table -&gt; Routing table -&gt; - analyser table
                                      - subcontractor table 
                                      - Interne user table 




Edit:, answers to questions in comments:


Can a task have many routings? Can a routing belong to many tasks or just one?
No, a task is routed to one routing (the routing is the manner to know where the task should be done).
Is there an Analyzer, a Subcontractor and an Interne (ManualWorker) table?
Yes, there is an analyser table, and subcontractor table, and interne table. 
Can an analyser be part of many routings (of the same task)?
Yes, an analyser can be a part of many routing. 
Can a subcontractor take part in many routings of the same task?
No, a subcontractor (or analyser or interne) take to one routing of the task (the task is routed to one subctr, or analyser or in interne).
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.