Today, unified modeling language (UML) has become a standard modeling language in object-oriented systems analysis and design. Specifying the business logic constraint with object constraint language (OCL) and transforming the specification into code has become a main trend in this area. This research presents a classification of OCL expressions to specify the attribute, operation and relationship constraint on Class diagram. A sample case and a CASE tool are used to test the usability (including the concepts, application, and advantages) of the proposed method. With this approach, the system developer can specify the constraints easily and transform them into code automatically and thereby enhance the efficiency and reusability of system development.