Declarative Development of Distributed Applications

Apart from traditional usage scenarios such as online shopping and browsing, the web continues to evolve to an active platform for distributed applications, e.g. implementing business processes. Standardized protocols and technologies, including Web Services, RSS/Atom feeds and REST, provide the communication infrastructure for the involved systems. They allow the integration of heterogeneous components and architectures, thus creating applications which exclusively communicate using XML messages and asynchronous transfer modes. Today, the individual nodes participating in those distributed applications are realized using imperative languages, such as Java or C#, and deployed on traditional, n-tier architectures. They involve a multitude of hardand software layers, including messaging solutions for remote communication, application servers running object-oriented programs, and (relational) database backends providing persistent storage. To support distributed applications and offer communication mechanisms such as SOAP and AJAX, these systems usually incorporate additional XML adapters and converters. However, they fail to efficiently support the requirements of distributed, XML-messaging applications. These include convenient, high-performance XML processing facilities and reliable, asynchronous messaging operations. As a consequence, development gets unnecessarily complex: