Hi all! I am trying to solve this problem for a while but i couldn't still solve it.

Let there be a company which has many service centers. I created a table which contains information about them:

Table "service_centers"
-----------------------
id (primary key)
name
address

Each service center makes some works, one can change tires on car, the other can repair engines, etc... I created a table which contains service types:

Table "service_types"
---------------------
id (PK)
name

... and bound it to "service_centers" table, to determine what kind of services each service center supplies:

Table "SC_ST"
-------------
id_service_center (references to service_centers.id)
id_service_types (references to service_types.id)

There are works related to each service type (for example, on "tire" service type the following works can be done: tire replacement, air pumping. On "engine" service type there could be "engine repairing", "oil changing"). So i created a table which contains all work types:

Table work_types
----------------
id (PK)
name

... and bound it to "service_types" table

Table ST_WT
-----------
id_service_type (references to service_types.id)
id_work_type (references to work_types.id)

Now i create a table which contains info on work done on all centers:

Table works
-----------
id (PK)
car_number
service_center_id
work_type_id

Seems like it's ok but i can't restrict entering wrong work types, for example:

Table "service_centers"
-----------------------

id                 name                   address
-------------------------------------------------
1                  servcen1               A st, 1
2                  servcen2               B st, 2
3                  servcen3               C st, 3

=========================================================

Table service_types
-------------------

id                name
------------------------------------
1                 tires
2                 engine

===========================================================

Table SC_ST
-----------

service_center_id           service_type_id
------------------------------------------------------------
1                           1
2                           2
3                           1
3                           2

==============================================================

Table work_types
----------------

id                          name
----------------------------------------------------------
1                           Tire replacement
2                           Air pumping
3                           Engine repairing
4                           Oil changing

================================================================

Table ST_WT
-----------

service_type_id             work_type_id
------------------------------------------------------------
1                           1
1                           2
2                           3
2                           4

===================================================================

Table works
-----------

id            car_number            service_center_id        work_type_id
--------------------------------------------------------------------------
1             123-4567              1`                       1
1             321-6547              1                        3 <-- Incorrect! Engine repairing 
                                                                   cannot be done on a service
                                                                   center which provides only
                                                                   "tire" service

And THE QUESTION IS:

How can i avoid this kind of problem? I tried to solve it by foreign keys, but seems like it's impossible.

Thank you.