A DBMS-based knowledge extension and inference service method recorded on a computer-readable medium includes creating knowledge represented as a triple by using ontology schemas and instances (first step); receiving the knowledge and extending the knowledge by using a knowledge extension rule (second step); and providing an inference service by using the extended knowledge, converting a user query, and processing the query (third step). Further, the third step includes receiving and converting a user query to create the converted query (31st step); determining whether the query is a previously-input query (32nd step); receiving the converted query and the determination result to create a query result (33rd step); receiving the query result of the 33rd step and performing post-processing to create a post-processing result (34th step); and creating a message and protocol suitable for a user interface by using the post-processing result and then presenting an inference result.