Visual Modelling of Semantic Services by Graph Transformation

Web服务的愿景意味着程序应该能够动态地(在运行时)定位和调用所需的服务。在Web服务中，预订机票、购买书籍、支付等功能可由机器以编程方式使用，而不是由人类用户手动使用。因此，Web服务遵循面向服务的体系结构(SOA)，该体系结构定义了提供者、请求者和中央发现服务的角色。提供商通过在发现服务上发布描述来宣传其提供的服务。当客户(请求者)正在寻找特定类型的服务时，他们查询该发现服务并接收合适的候选者列表。在选择了最合适的服务后，客户可以通过联系提供商直接使用该服务。面向服务的应用程序的分布式和动态特性给它们的开发带来了新的挑战。-如何指定服务提供的功能和客户端应用程序所需的功能和行为，并验证它们是否匹配？-当动态发现和绑定违反静态验证和集成测试的基本假设时，如何确保服务和客户端应用程序之间的互操作性？-如何处理这样的事实：虽然服务与请求者和提供者使用的技术无关，但其实现与周围的IT基础设施集成？这些挑战的解决方案通常分为两类。数据驱动的方法：本体用于描述服务的输入输出关系，或根据前置和后置条件和不变量对其自身数据状态的影响。这样的条件可以用高级逻辑规范语言表示，供人类使用，但为了在运行时自动进行发现和绑定，规范需要是机器可读的形式。OWL-S等基于描述逻辑的服务语义Web语言满足了这一需求。流程驱动的方法：可视化模型(基于统一建模语言或业务流程建模符号)描述服务的行为。这样的模型会自动转换为基于XML的描述(例如，在WSDL或WS-BPEL中)。这种方法提供了与主流软件开发实践的一致性，但由于可视化模型的半形式化特征，它们不能完全解决互操作性问题。形式化的流程描述方法(例如，基于流程演算)在实践中并没有直接使用，尽管它们确实为特定于域的语言(如WS-BPEL)的设计提供了信息。在这个提案中，我们建议将基于描述逻辑和面向流程的技术的服务描述的形式化特征与UML的直观可视性质以及两者之间的自动转换思想结合起来。在这方面，我们的目标不仅是在模型级别产生描述和产生基于逻辑的表示，而且-更好地将数据(本体)的规范与行为(过程)的建模相结合；-在可视化模型级别支持对服务的互操作性的推理，从而允许代表领域专家对匹配和选择服务所涉及的机制有更深的理解。

The vision of Web services, where functions like booking flights, buying books, making payments, etc. are available to be used programmatically by a machine, rather than manually by a human user, implies that programs should be able to locate and invoke required services dynamically (at runtime). Web services therefore follow the service-oriented architecture (SOA), which defines the roles of provider, requestor, and central discovery services. Providers advertise their offered services by publishing descriptions on a discovery service. When clients (requestors) are looking for a specific kind of service, they query this discovery service and receive a list of suitable candidates. After selecting the most suitable services, the client is able to use the service directly by contacting the provider. The distributed and dynamic nature of service-oriented applications raises new challenges for their development. - How to specify the functionality and behaviour both provided by a service and required by a client application, and verify that they match? - How to ensure interoperability between services and client applications when dynamic discovery and binding violates the assumptions underlying static verification and integration testing? - How to handle the fact that that, while services are agnostic of technologies used by requestor and provider, their implementations are integrated with the surrounding IT infrastructure? Solutions to these challenges generally fall into one of two categories.Data-driven approaches: Ontologies are used for describing services' input-output relation, or effects on their own data states, in terms of pre- and post conditions and invariants. For consumption by humans such conditions can be expressed in a high-level logical specification language, but for discovery and binding to happen automatically at runtime, specifications need to be in machine-readable form. Semantic web languages for services like OWL-S based on description logics satisfy this requirements.Process-driven approaches: Visual models (based on the Unified Modelling Language (UML) or the Business Process Modelling Notation (BPMN)) describe services' behaviour. Such models are transformed into XML-based descriptions (for example in WSDL or WS-BPEL) automatically. Such an approach provides alignment with mainstream software development practices, but due to the semi-formal character of visual models they cannot fully address interoperability issues. Formal process description methods (for example based on process calculi) are not directly used in practice, although they do inform the design of domain specific languages like WS-BPEL. In this proposal we suggest to combine the formal character of service descriptions based on description logics and process-oriented techniques with the intuitive visual nature of UML and the idea of an automatic translation between the two. In this, we do not only aim at producing descriptions at the model level and generating the logic-based representations, but also - to integrate better the specification of data (ontologies) with the modelling of behavior (processes);- support reasoning on the interoperability of services at the level of visual models, thus allowing a deeper understanding on behalf of domain experts of the mechanisms involved in matching and selecting services.