Data modeling, double foreign key problem I have a certain problem, while creating logical/relational model of database. I get duplicate foreign key in a table. This table is referencing 2 other tables, thorugh identyfing relationship, which reference this particular key and they have to be primary keys because they are cross-reference tables.
Something like this:

How can i fix this so i don't have duplicate keys on PARAM_VAL: id_quali1 and id_quali?
Like @J.D. mentions in his comment it is not obvious what problem you are trying to solve. If I were to guess PARAM_VAL could be consructed as:
CREATE TABLE param_val
( id_quali ... NOT NULL
, id_param ... NOT NULL
, id_cand ... NOT NULL
, PRIMARY KEY (id_quali, id_param, id_cand) -- I guess
, FOREIGN KEY (id_quali, id_param) 
      REFERENCES param_weight(id_quali, id_param)
, FOREIGN KEY (id_quali, id_cand) 
      REFERENCES quali_participation(id_quali, id_cand)
);