DB-Prolog is an extended version of Prolog which allows users to access relational databases in both evaluational and non-evaluational approaches. Using the former approach, DB-Prolog offers some built-in predicates for retrieving relational databases. Using the latter approach, DB-Prolog enables relational databases to store facts (ground unit clauses) which may have compound terms in their arguments. As a result, DB-Prolog can execute Prolog programs which contain both a large set of facts, and conventional data (both numerical and character) efficiently. These Prolog programs are required for the construction of practical expert systems. DB-Prolog implementation techniques are described, and some of its available functions are discussed.