The Internet of Things environment has offered both the expediency and valuable information to users as its services with physical objects which are in size from small devices (sensor, actuator etc.) to big (Smart Camera, Smart Car, Smart Refrigerator etc.). In the part of services offer, a specific service which can be utilized for users should be composed of several kinds of devices and have an ability to both be connected and communicate with each other. Furthermore, these services must be reliable since it has potential to be offered that is not suitable for each user. For making possible to it, many studies have gone off in Internet of Things. The middleware structure can integrate information from all kind of devices and have abstract layers to maintain user's information and devices status. However, a system for responding to tremendous users with reliable services in real-Time on Internet of Things' environment still is a great challenge in terms of limited resources. The goal of this paper is to discuss these challenges and propose new directions for solutions at the middleware layer. We take a directed graph composition scheme for service object in Internet of Things to make services efficient and trustworthy. From the advantage of our proposed structure, most of scenarios in the Internet of Things can be dealt with it.