With the increasing popularity of Object-Relational technology, it becomes necessary to have a methodology that allows database designers to exploit the great modeling power of object-oriented conceptual model, and still facilitate implementation on relational database systems. This paper presents a transformation methodology from inheritance relationships to relational tables. This includes transformation of different types of inheritance, such as union inheritance, mutual exclusion inheritance, partition inheritance and multiple inheritance. Performance comparison between the proposed transformation methodology and existing methods is also carried out. From the evaluation, we conclude that the proposed transformation methodology is more efficient than the others.