The world today is characterised by the proliferation of information sources available through media such as the WWW, databases, semi-structured files (e.g. XML documents), etc. Nevertheless, this information is usually scattered, heterogeneous and weakly structured, so it is difficult to process it automatically. DENODO Corporation has developed a mediator system for the construction of semi-structured and structured data integration applications. This system has already been used in the

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... uction of several applications on the Internet and in corporate environments, which are currently deployed at several important Internet audience sites and large sized business corporations. In this extended abstract, we present an overview of the system and we put forward some conclusions arising from our experience in building realworld data integration applications, focusing in some challenges we believe require more attention from the research community.