DBI to pick Manager salary

Summary

Written the following formula to pick the manager salary, giving no value. Seems I am using the wrong DBI.

Content

/*=========== DATABASE ITEM DEFAULTS BEGIN ==============*/
DEFAULT FOR L_MGR_NUMBER IS ' '
DEFAULT FOR PER_ASG_PERSON_NUMBER IS ' '
DEFAULT FOR CMP_ASSIGNMENT_SALARY_AMOUNT IS 0
DEFAULT FOR PER_ASG_MGR_MANAGER_ID IS 0
/*=========== DATABASE ITEM DEFAULTS END ================*/
/*=========== INPUT SECTION BEGIN ==============*/
INPUTS ARE CMP_IV_PLAN_ID (number)
/*=========== INPUT SECTION ENDS ==============*/
/*=========== FORMULA SECTION BEGIN =====================*/
L_MGR_NUMBER = to_char(PER_ASG_MGR_MANAGER_ID)
CHANGE_CONTEXTS(PERSON_ID = TO_NUMBER(L_MGR_NUMBER))
(
RULE_VALUE = CMP_ASSIGNMENT_SALARY_AMOUNT