## 2 Related Work
To solve the aforementioned problem, streaming in a service-oriented way has already been addressed very early in some papers. In [13] the authors extend Simple Object Access Protocol (SOAP) messages by introducing additional attributes inside the SOAP envelope. With these attributes it is possible to support boxcarring and batching of messages. After SOAP had become a standard, [17] described another early Web service based approach which relied on the upcoming standard Direct Internet Message Encapsulation (DIME). In this architecture, the SOAP messages were used for delivering the multimedia content metadata and the multimedia content itself was delivered by using DIME. However, DIME has since been withdrawn and was never given a request for comments (RFC) status. Another efficient method for sending binary data to and from Web services is the Message Transmission Optimization Mechanism (MTOM) [18], implementing XML-binary Optimized Packaging (XOP) for SOAP messages. MTOM uses the multipurpose Internet mail extensions (MIME) to package the message after XOP processing. But nowadays SOAP Messages with Attachments (SwA) are quite popular and are for instance used in the architecture described in [19]. Here a new Message Exchange Pattern (MEP) for streaming data is defined and this MEP is then implemented in the SOAP Hypertext Transfer Protocol (HTTP) binding. Using SOAP with attachments, a single multimedia data segment can be transmitted as a SOAP message package which can include as many parts as needed. A current approach introduces a service-oriented infrastructure for multimedia processing using Flex-SwA [7] and is described in [20]. In the Web service business world, although business process execution languages (like e.g., Business Process Execution Language (BPEL) [21], Yet Another Workflow Language (YAWL) [22], or Business Process Modeling Notation (BPMN) and workflow management systems are closely related. However, the workflows we use in the multimedia domain are not comparable to the business process models, and thus, the available languages are not readily applicable. The main difference to general purpose languages is the inclusion of continuous data streams in our workflows. Only a few extensions to Web service description languages to support continuous data streams exist. Again, most are not yet considered to be ready for use [19, 23, 24]. Moreover, the workflows currently needed by our architecture are simple compared to the flexibility of the modeling constructs available in the general purpose workflow frameworks. As a result, we use our own Resource Description Framework (RDF)-based workflow model and language with added support for describing the streaming of data between participants. For the actual instantiation systems already exist, such as IRS-III [25], which can create service compositions using goal based reasoning. However, creating and maintaining the domain ontology needed for the reasoning process is a complex and time-consuming task. As a result, our system works on an extensible set of template workflows for the most common multimedia applications. In order to describe the capabilities of our multimedia services, OWL-S [26] was chosen on the premise that it is an established standard for semantic Web services. Furthermore, it allows the selection of Web services not only based on their WSDL description [27]. In contrast, OWL-S service descriptions do not only contain information about the invocation of a service, known as service grounding. They also contain information about \"what a service does\", and \"how it does it\", known as service profile and service process model, which allows to select services based on capabilities. Such semantic matchmaking techniques have been investigated, e.g., in [28, 29]. To our knowledge, the only system to actually validate interoperability between Web services was developed by [PERSON] _et al._[30]. It uses a translation of choreographies and orchestrations into finite state automata, in this case a labeled transition system.