Research On Key Techniques Of Service-oriented Middleware For Pervasive Computing

Applications used in pervasive computing environments must be applicable in error-prone physical devices with limited resources. Also, they must be adaptable to the changeful environments of pervasive computing. By far, no software infrastructure that wholly supports pervasive computing has been realized. This paper focused on the dynamic configurability and heterogeneity support of software infrastructures designed for pervasive computing, analyzed the state of the art in middleware technology, discussed features and challenges of pervasive middleware, and proposed a service-oriented pervasive middleware architecture based on improved Dynamic Object Model (DOM). We aimed to propose a software infrastructure (DOM-based middleware for short) that could meet requirements of pervasive computing and facilitate the development of pervasive applications. Experiments made on the prototype middleware system called 'Mix' showed the performance of the DOM-based middleware architecture.The original DOM didn't specify the way to abstract object types. One object type might include many types of behaviors, which made it hard to establish standards for abstraction of object types and sharing knowledge of different domains. So we improved the original DOM, introduced a new concept called 'behavior' into the model, clarified the way to abstract object types based on attribute types and behavior types, and discussed the model's reflective capability and dynamic configurability.The DOM-based middleware architecture mainly contains four layers: environment layer, object layer, service layer and task layer. The object lay takes the responsibility to implement and manage DOM. The service layer is the place where main functional logics of middleware are implemented. Protocol layer is an auxiliary to the service layer which helps realize multiple service discovery protocol (SDP) and multiple service invocation protocol (SIP) support. Dynamic objects are key components of the DOM-based middleware and services deployed.Pervasive middleware not only have to overcome the problem of interaction between heterogeneous SDPs, but they also have to fuse heterogeneous SIPs. Currently, there are many proposed SDPs and SIPs. Although, these protocols can fulfill some requirements of pervasive computing, none of them can meet all the requirements. Multi-protocol support may be the only approach to realize efficient service discovery and service invocation in different network environments. Multi-protocol support for service discovery and service invocation in DOM-based middleware proposed in this paper was implemented by protocol executors, which acted as adapters between the service manager and protocols.The interchangeability of attributes, behaviors and dynamic objects makes the improved DOM highly dynamic configurable; as all SDP (or SIP) executors have the same public interface, SDPs (or SIPs) are interchangeable during runtime; by separation of service discovery framework, service invocation framework and service migration framework, DOM-based middleware made it possible for different types of protocols to work together. All these new ideas proposed in this paper made DOM-base service-oriented middleware adaptable to changefulness and heterogeneity of pervasive computing environments.