Component composition and Web-service composition have in common that the usage pattern of a certain black-box component or Web-service needs to be described precisely. Because usually many interactions between the client and the service provider are required to obtain a certain desired functionality, one would hope to find the specification of permissible interaction sequences with the service provider in service description formalisms, such as the WSDL. This paper shows an approach to automatically generate such interaction specifications for service descriptions from the XMI representation of UML sequence diagrams. It uses an algebraic representation based on path expressions, which are incorporated into the WSDL. The paper further argues for their value at design- and runtime.