5. The knowledge base system according to claim 1 , wherein said operation unit is configured to, when one entity is designated as an operation target, perform the logic operation on an attribute of the designated entity.
13. The knowledge base system according to claim 5 , wherein said operation unit is further configured to, when two attribute sets each of which includes one or more attributes are designated: count, in a case where each attribute is associated with a true-false value indicating whether the attribute is true or false, a number of attributes that have a same primary identifier and are associated with a same true-false value between the two attribute sets, as a degree of similarity; and count, in a case where each attribute is not associated with the true-false value, a number of attributes that have a same primary identifier between the two attribute sets, as the degree of similarity.