Automated Runtime Testing of Web Services

Service-oriented computing (SOC) is a relatively new paradigm for developing software applications through the composition of software units called services. With services, software is no longer owned but offered remotely, within or across organisational borders. Currently, the dominant technology for implementing services is that of Web services. Since service requestors do not usually have access to the implementation source code, from their perspective, services are offered as black boxes. However, requestors need to verify first that provided services are trustworthy and implemented correctly before they are integrated into their own business-critical systems. The verification and testing of remote, third-party services involve unique considerations, since testing must be performed in a blackbox manner and at runtime. Addressing the aforementioned concerns, the research work described in this thesis investigates the feasibility of testing Web services for functional correctness, especially at runtime. The aim is to introduce rigour and automation to the testing process, so that service requestors can verify Web services with correctness guarantees and with the aid of tools. Thus, formal methods are utilised to specify the functionality of Web services unambiguously, so that they are amenable to automated and systematic testing. The well-studied stream X-machine (SXM) formalism has been selected as suitable for modelling both the dynamic behavior and static data of Web services, while a proven testing method associated with SXMs is used to derive test sets that can verify the correctness of the implementations. This research concentrates on testing stateful Web services, in which the presence of state makes their behaviour more complex and more difficult to specify and test. The nature of Web service state, its effect on service behaviour, and implications on service modelling and testing, are investigated. In addition, comprehensive techniques are described for deriving a stream X-machine specification of a Web service, and for subsequently testing its implementation for equivalence to the specification. Then, a collaborative approach that makes possible third-party Web service verification and validation is proposed, in which the service provider is required to supply a SXM specification of the service functionality along with the standard WSDL description of its interface. On top of that, techniques are proposed for service providers to include information that ground the abstract SXM specification to the concrete Web service implementation. Having these descriptions available, it is possible to automate at runtime not only test set generation but also test case execution on Web services. A tool has been developed as part of this work, which extends an existing SXM-based testing tool (JSXM). The tool supports the tester activities, consisting of generation of abstract test cases from the SXM specification and their execution on the Web service under test using the supplied grounding information. Practical Web service examples are also used throughout the thesis to demonstrate the proposed techniques

Influencing the run-time behaviour of complex services using contexts

Service oriented architecture (SOA) and web services make it possible to construct rich and complex distributed systems which operate at internet scales. However, the underlying design principles of SOA can lead to management problems for processes over web services. This thesis identifies several potential problems with the management of processes over web services, and proposes the use of explicit context as a possible solution. The available options are explored, and the WS-Context specification is implemented and evaluated. The SOA design principles of loose coupling, interaction at an interface, autonomy, and composablity can lead to management problems for processes over web services. Processes over web services where one composite service invokes other composite services which in turn invoke other composite services can lead to complex invocation trees. These invocation trees may be different at different times due to the shifting effect of loose coupling, as new services are swapped in to replace those in previous invocations. In such an environment how well can we define the interface of the top level service in a static document such as a WSDL? Because there is a separation between the ultimate service consumer, and the ultimate service provider how can the service consumer correctly assign fault when a service fails? When concurrency is used, and encouraged, how can we deal with the inevitable race conditions and deadlock? In distributed systems where portions of processes execute on systems beyond our organizational control, how can we pause, or kill these processes? Many of these systems model long-running business processes. How do we communicate changes in process requirements? The use of an explicit context is a potential solution to these types of problems. The abstraction context provides an environment in which the process participants can describe their requirements, query those of other process participants, and react to changes in the environment. A sample context server, based on the WS-Context specification, was implemented using the Erlang language. The sample context server provides the basic operations required to manage and store contextual information about a process. The sample context server was evaluated to determine the cost of employing a context as part of a web service based software system. The performance of the sample server was also evaluated. Test were conducted on the time costs of the basic operations of the context server, and they were found to have a constant time cost. The operations for getting and setting the contents of the context were found to have a time cost dependant on the size of the context. The cost of propagating the context along a chain of service invocations was tested and found to have an overhead which increased linearly with the length of the service invocation chain. The context server was stress tested using a closed loop test which simulated the interaction of a number of concurrent clients, and an open loop test which simulated bursts of arriving requests. The open loop testing showed that the context server could handle 75 concurrent clients. Beyond 75 concurrent clients, the response times of the context server began to slowly increase. The closed loop testing showed that the context server had a maximum throughput of 190 requests per second for bursts of 200 requests with an interarrival time of 4 milliseconds

Gaywaves: Transcending Boundaries - the Rise and Demise of Britain's First Gay Radio Program

At the beginning of 1982 an array of conflicting forces were working to shape the landscape of Europe's metropolitan radio services, and to alternatively control, commodify or liberate its gay communities. This paper examines the drivers, which inspired Gaywaves, a nascent weekly gay community radio programme broadcasting to an inner London audience on pirate station Our Radio from May 1982 until March 1983