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niversal Description, Discovery and Integration (UDDI) standards [46,61]. Interaction amongst these three roles is supported by the service platform which provides facilities for service composition (Steps 2 and 3) and service execution (Step 4) for fulfilling service requests (Step 1). The relationship between WSDL and UDDI is shown in Fig. 2. A business entity in UDDI indicates information about the business that may provide services such as names and contact information. A business service contains descriptive information about services such as service names and narratives. Business services may utilize business classification codes such as UNSPSC and NAICS [58 marlboro menthol cigarettes,59]. Implementation-specific information on the service is described in the binding template. Binding templates include a tModel—technology model which contains machine-readable, implementation-specific information newport cigarettes online, on the business and a pointer to the actual service location defined by an access point. The machine-
readable WSDL descriptions provide a minimal explicit characterization of the services in terms of both an implementation and interface definition. WSDL is adequate for describing elementary services as it takes a stateless view of services with welldefined inputs and outputs. From the URL provided by the access point, one may retrieve the WSDL which encodes actual information about the service and use the interface definition to enable appropriate exchange of SOAP messages. In summary, the metadata about services provided by UDDI includes a reference to a service description (WSDL) based on an predefined service taxonomy. Customers request services from service platforms. The service platforms execute the task of locating tModels and acquiring the necessary WSDL descriptions. Services are located based on possibly registry-specific UDDI taxonomy and the actual description (the WSDL) is obtained via the access point. For example cheap newport cigarettes, services S1, S2, S31 and S32 publish to the UDDI registry. Services may be composed in advance newports cigarettes website, registered by a service provider and used to service multiple requests. For example, service S3 composed of services S31 and S32 may be predefined manually by an intermediary provider. However, under volatile conditions, such
Fig. 2. Relationship between UDDI and WSDL.
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T. Madhusudan, N. Uttamsingh / Decision Support Systems 41 (2006) 325–357
advanced composition may be unreliable during execution if component service capabilities or predefined assumptions on the composite behavior required change. Recent research has focused on developing advanced service composition and execution components of the service platform of Fig. 1. Scaling up utilization of web services in open, dynamic environments would require automated support for service design, service redesign and execution. We provide an overview of major challenges in facilitating automated service composition and discuss the applicability of AI planning techniques to this task. Additionally, we also consider the dynamics of the execution env