There is probably no invention in the history of mankind that had such a profound impact on our lives in such a short time as the World Wide Web. Twenty years ago, Tim Berners-Lee has developed the first versions of HTML which allowed to weave documents into the large hypertext document that we know today. It was soon realized that the potential of this technology is not limited to connecting texts, but may serve as a backbone for a world-wide knowledge base called the Semantic Web. Again, Tim Berners-Lee helped to pioneer the vision of data and knowledge being publicly available in a formalized, machine-processable form. Based on standards like RDF or OWL, knowledge and semantics may be freely exchanged between heterogeneous applications. The number of facts stored in public knowledge repositories, so-called ontologies, is increasing at a rapid scale. Linked open data are on the verge of permeating our everyday lives.

Now we are facing the next revolution. Not only documents or knowledge will be connected, but computer applications are no longer running on personal computers, but on centralized servers which can be accessed via Web interfaces from a large variety of processors in smartphones, TVs, cars, household appliances, and more. For the end user, this not only relieves them of the burden of the update and maintenance of their software, but allows them to access their applications in a uniform way, everywhere and at every time.

A grand challenge for web-based software design is to integrate different heterogeneous applications into a homogeneous new system that utilizes the familiar existing components but allows a transparent data exchange between these components. Such Mash-Ups can be realized at the code level, by reprogramming functions of the individual applications, or at the data or business logic level by formalizing the service description and access of the applications, e.g. in the form of Web Services. Both ways have the disadvantage that aspects of the application have to be reprogrammed in order to allow a standardized data exchange.