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An Internet application can invoke several services--a stock-trading Web service, for example, could invoke a payment service, which could then invoke an authentication service. Such a scenario is called a composite Web service, and it can be specified statically or established dynamically. Dynamic composition of Web services requires service consumers to discover service providers that satisfy given functional and nonfunctional requirements including cost and QoS requirements such as performance and availability. In previous columns, I've examined how quality of service (QoS) comes into play for service providers, consumers, and parallel transactions. Here, I'll show how it fits into composite Web services.