1. A knowledge base system comprising: a storage unit in which a knowledge base is stored; and an operation unit configured to perform a logic operation on the knowledge base stored in said storage unit, wherein the knowledge base includes a plurality of entities, each of the entities including an entity identifier for identifying an entity and includes one or more attributes of the entity, the one or more attributes being associated with the entity identifier of the entity, the one or more attributes each includes: an attribute identifier for identifying the attribute; and at least one of (i) a feature data identifier and feature data and (ii) an identification data identifier and identification data, the feature data being one or more pieces of data representing the attribute and being associated with the attribute identifier for identifying the attribute, the feature data identifier identifying a memory address in which the feature data is stored, the identification data being data associated with a word representing the attribute and being associated with the attribute identifier and the identification data identifier identifying the identification data, the entity identifier is not a word representing the entity, and is made of a symbol that has no meaning per se, and the attribute identifier is not the word representing the attribute, and is made of a symbol that has no meaning per se, the attribute identifier being an identifier which independently indicates the attribute without depending on a hierarchical classification of previously generated knowledge, such that the attribute identifier identifies the attribute of the entity without any dependency on another attribute of the entity.