The aim of this work is to develop a template for component-based
 programs which can be used in different programming languages.
 First, we give a model of component based systems based on the
 unifying theory of programming. We define the concepts interface,
 contract and component, and component combination. The definition can
 be used as the basis for the component template development. We
 define a contract to include method specification, and define a
 component as an implementation of a contract. This implementation may
 require services from other components with some assumptions about
 the schedule for resolving the conflict of shared method and resource
 uses with the presence of concurrency. The assumption is expressed as
 interaction protocols. In our model, components are correct by its
 design. We then give a guideline for extending the model for
 real-time component systems.