A Web service is represented as a component that you can display in a component diagram. From a component diagram, you can display the Web service interface and implementation code, eventually, you can also deploy Web service components to nodes if you want to describe deployment of components into servers.
For more information on how to deploy components, see Deploying a Component to a Node.
A component can be a Web service Interface or a Web service Implementation type. You have to check the Web Service check box in the component property sheet to declare your component as a Web service.