Research On QoS Based Dynamic Composition Of Semantic Web Of Things Service

Through the information sensing devices, the Semantic Web of Things introduces physical entities with identity, perception and executive ability into the Internet. And based on ontology for semantic-annotation and support-understandability, it also publishes the functions in the form of services on the Internet. Compared with the Web services, the Semantic Web of Things services have great difference in the service description, service environment and service resources. So that the simple atomic services which are provided by resource-constrained physical devices can not meet the complex service requests which are caused by heterogeneous and distributed in the Semantic Web of Things. In order to solve the problem above, this paper presents a method to QoS based dynamic composition of Semantic Web of Things services to provide more accurate services for service requester according to different service objects and different service environment dynamically.This paper is based on the QoS ontology to realize the dynamic combination of Semantic Web of Things service. Firstly, it constructs the context-appended QoS ontology according to QoS parameters, context parameters and the mutual influence and restricting relation between them. Based on the context-appended QoS ontology, it also generates QoS limited and standardized description file of Semantic Web of Things service without semantic conflict. Secondly, it applies dimensionless method to the QoS parameters in the QoS limited service description file and carries out atom matching and aggregation matching to get the candidate service set. Then, it constructs the directed graph which takes services, the input data and output data as nodes, uses the QoS variable to record changes of QoS parameters in the process of dynamic service composition and carries out the new combination services through graph search method. finally, it maps the new service to the corresponding virtual objects to form the Web of virtual objects, through which physical equipment can feedback the service request results to the service requester.In order to verify the effectiveness of this method above in the Semantic Web of Things, this paper designs and implements a QoS based dynamic Semantic Web of Things service composition protosystem. The system which includes a service preliminary selection model, QoS constrained service description file generation module, QoS based service selection module, graph search based service composition module and WoO based service mapping module realizes the selection, combination and mapping functions of Semantic Web of Things service. Finally the comparative analyses of specific example show that this method can provide more accurate services for service requester according to different service objects and different service environment dynamically.