The Web is continuously being transformed from a web primarily aimed at human consumption to a web of data which will allow autonomous agents to carry out complex reasoning tasks for humans. An indispensable ingredient for this transformation is rule based data integration of semi-structured web content in its various formats, such as HTML, XML, RDF and Microformats. By introducing the framework of Rich Unification, this thesis shows how existing rule languages can be adapted to fulfill the needs for data integration on the Web. It is shown that SPARQL, XPath and Xcerpt neatly fit into this...