Design and Implementation of a Database Programming Language for XML-based Applications

XML is the de facto standard for data exchange between arbitrary applications. These applications are written in object-oriented programming languages like Java or C# for example. Consequently the need arises to integrate XML into existing object-oriented programming languages. Moreover, many applications have to keep and deal with persistent data and objects. A lot of frameworks are currently being developed which are trying to solve mismatch problems between the transient object model and the persistent data model. Due to performance reasons relational databases are taken in general. Although existing approaches try to minimize the mapping effort, true transparent persistency is not gained at the moment. In this work transparent persistency means that objects can be stored regardless of type, algorithms remain unchanged whether they operate on persistent or transient data and finally that programmers, if at all, deal with persistency on a very high level. In addition many persistence solutions do not even support the main object-oriented concepts like inheritance and polymorphism. As well object-oriented databases are limited to a single programming language and are rarely available. All that the frameworks or approaches mentioned so far have got in common is that the programmer has to add special code when dealing with persistent objects or classes. The code includes communication with a so-called persistency manager for example. In the past several database programming languages have been developed, but they all have tried to integrate the relational model. Consequently, a holistic and transparent solution is needed that integrates XML and persistency into an existing object-oriented programming language. In this work XOBEDBPL (XML OBjEts DataBase Programming Language) is developed as an extension of the object-oriented programming language Java. XOBEDBPL is based on its predecessor project XOBE. In XOBE XML and XPath are already integrated and checked statically at compile time against an XML schema. XML Schemas and DTDs are supported as XML schema description languages. In XOBEDBPL XML objects can now be manipulated with the help of updates. Moreover the type checking process of XOBE is extended to support updates and more complex queries as well. Additionally, transparent type independent persistency supporting all object-oriented concepts is introduced in XOBEDBPL for the first time. The prototypical implementation is based on a persistency layer using web services. The persistency layer keeps persistent objects and data and offers the possibility to exchange data among arbitrary languages and applications. Moreover, it is shown that the introduced concepts can also be realized as a semantical extension of Java. Consequently programmers do not have to learn