## 2 Intelligent Service Broker  
Authors propose the Intelligent Services Broker (ISB) as a reference example of an adaptive computing system. The goal of the ISB is to aggregate the information about available services in the information space and deliver the best quality of service (QoS) for consumers that are placed in a certain context by means of intelligent services composition.  
At the initial step, the available services and consumers shall be provisioned in the ISB. Service providers have to present profile description for what they offer. These profiles contain description of the service functionality and the context required for services to operate. Consumers fill-in their static profile with demographic data, interests and preferences; in addition to that, the ISB collects dynamic data about subscribers. Users' geographic coordinates, their services consumption behavior and other types of context information can be collected for better targeting of the services promotion.  
At runtime, the ISB analyses the current context for subscribers and their requirements, and optimizes the services composition offer for delivering the best QoS in the present situation taking into account resources available for the system.  
The users' requirements can be defined explicitly, for example, expressed verbally or entered as a plain text; and implicitly - derived from the users' preferences.  
The ISB is architecturally decomposed for two layers, see Figure 1. Network infrastructure, required hardware, and available sensors are depicted at the bottom layer. On the upper abstraction layer one can see a collection of the software components that serve as a mapping of the available services, sensors, and registered end-users to the virtual space. In other words, each consumer has its digital software agent as well as every sensor, and all services offered by the service providers.  
The software components organize clusters dynamically on demand for collaborative work in order to fulfill the needs of subscribers. For example, on the diagram we can see a cluster of red colored components that represent a service composition for the correspondent red-colored consumer.  
Let us consider an illustrative end-user scenario where the ISB helps subscribers with their everyday life issues. An ISB subscriber [PERSON] is walking in a city's downtown. He is carrying a mobile device that connects him to the virtual information space managed by ISB. [PERSON] stated in his profile that he is interested in the topic of self-organizing systems and would be interested to meet new buddies with similar interests. Passing by the bookstore that is provisioned in the ISB, [PERSON] receives a notification message regarding the sale in the shop and availability of the items of his interest.  
After entering the bookstore [PERSON] is able to read the virtual messages left there by other customers that also involved in the same research. The virtual messages are posted in a certain situation. The message originator defines the condition in which the message can be read. In our use-case, message has been left in the bookstore, and can be accessed at certain time by selected group of people.  
With support from ISB, the software agent \"_alex_\" is forming a cluster with the \"_bookstore_\", \"_positioning sensor_\" and the \"_virtual bulleting board_\" software components for delivering the relevant services experience for the user. After some time, [PERSON] is leaving the store and going to a meeting with his friends. The ISB is providing a trip navigation service; therefore the cluster is to be reconfigured according to the new context and needs.  
The following sections of the paper are devoted for description and comparison of alternative mechanisms for the intelligent services composition.