Service-oriented computing systems have been issued by their properties of reducing software development time and effort by reusing functional service units. The reusability of services can effectively promote through loose coupling between services. But strong associations of object-oriented systems such as inheritance and aggregation create a rather tight coupling between objects. The component-based systems without inheritance and aggregation create a loose coupling between components. Thus components provide service realization at runtime using the functionality provided by their interfaces. Therefore legacy component-based systems need to have service-oriented computing concept in order to support functional service units efficiently. Also, conventional methods for service-oriented computing system have not suggested the clear classification of service layers, the clear service identification guideline introducing service layers and a service mapping method between serviceces of each layer. Therefore we suggest the service classification and the identification guideline of business view and implementation view introducing layers and propose a mapping between two views. That is, we research service layers, service identification, diversified service sizes and a service mapping method between services of each layer. This can be applied to legacy component-based system to extend to the service-oriented computing system.