While Sig.ma is by no mean the first data aggregator for the Semantic Web, its contribution is to show that the sum is really bigger than the single parts and exciting possibilities lie in a holistic approach for automatic semistructured data discovery and consolidation.
Read about Sig.ma on Journal of Web Semantics: Giovanni Tummarello, Richard
Cyganiak, Michele Catasta, Szymon Danielczyk, Renaud Delbru, Stefan
Decker "Sig.ma: Live views on the Web of Data", Journal of Web
Semantics: Science, Services and Agents on the World Wide Web - Volume
8, Issue 4, November 2010, Pages 355-364