Defines two keys, one defined on the input's data, the second on the data of another input. The analysis checks whether the key can be considered a foreign key in relation to the other (parent) entity coming from the second input. The result of analysis consists of three basic counters - the number of keys which are unique in the parent, the number of keys not unique in the parent and the number of keys not found in the parent. This means that the condition for foreign key quality is that the second and third counters are empty or very low.