Schema mappings are fundamental notions in data exchange and integration for relating source and target schemas. Visual mapping languages provide graphical means to visually describe such transformations. There is a plethora of tools and languages available however all use different notions and visualizations and are hardly extensible. In this paper we propose a new universal layer Umap for schema map ping languages which provides a unified abstraction and middleware for high-level visual mapping languages. We use only standardized Uml and Ocl artifacts which allow for easy code generation in a number of target languages (e.g. C++ code) and for a modular extension mechanism to support complex schema mappings. We illustrate our layer by translating key elements of Clip, a recent expressive visual mapping language, and show that Umap has enough expressive power to encode all Clip features. Moreover, we outline a strategy for automating the translation of any visual input language with a formal meta-model to Umap.
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