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ng execution newport cigarettes supplier, operators can time out due to network or source dynamics or plan execution can be interrupted to accommodate new customer requests. When failures or interruptions occur during execution, two options are available on resumption—(a) re-execute the remaining steps of the plan from current state or (b) re-plan to find a new alternative plan and then execute. The choice between these two options is usually not clear and depends on the environmental conditions. Developing optimal strategies for such different scenarios is a long-term research goal. The issues are further discussed in Section 5. When execution failures occur, the execution module updates the current state and chooses one of the above options as shown in Fig. 3. The cycle is repeated until a preset time limit expires or a successful answer to the service request is obtained.
5. Evaluation of IS P&E Based on our proposed approach, we have implemented the IS P&E system as a proof-of-concept prototype. The focus of our implementation has been on developing the planning and execution modules of the service platform. The architecture of the implemented system is shown in Fig. 13. The service
T. Madhusudan, N. Uttamsingh / Decision Support Systems 41 (2006) 325–357
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Fig. 13. IS P&E architecture.
platform consists of three main components, the planning module, the execution module and a world monitor that is monitoring the web services for dynamic information. For the planning module wholesale newport cigarettes, we have utilized the SHOP system implemented in Common Lisp and run as a LISP servlet. Further, the execution module is also implemented as a JAVA-based servlet and coordinates with the planning module. The generic steps are indicated by the numbers on arrows. The service request is issued in a browser and sent to the planning module (Step 1) cheap newport cigarettes, a service plan is generated and sent to the execution engine (Step 2), during execution service operations and platform operations are executed at the execution module (Step 3) and finally a result is returned to the user (Step 4) or if failure occurs, re-planning is considered (Step 5). In our current implementation, description about web services in the world is managed at two sites in the ISP&E framework: (1) in the service catalog maintained at the service platform discount newport cigarettes, and (2) in the world monitor maintained as part of the execution framework. The service catalog maintains the declarative description of the WSDL functions and their procedural mappings. The world monitor maintains the dynamic information and accesses statistics about each web service such as uptime since last failure, current availability and number of method calls. These two descriptions mimic UDDI to provide
design-level and execution level support. The service platform catalog is initialized manually in our current testbed. In future work, we aim to enable dynamic ontology update based on the semantic web capabilities as suggested in [40]. The world monitor is a multithreaded JAVA object maintaining real-time proxies of all the