Pattern-based relation extraction methods (e.g., (Davidov and Rappoport, 2008;Davidov et al., 2007;Banko et al., 2007;Pasca et al., 2006;Sekine, 2006)) could in theory be used to extract relations represented by commas.
the types of patterns used in web-scale lexical approaches currently constrain discovered patterns to relatively short spans of text, so will most likely fail on structures whose arguments cover large spans (for example, appositional clauses containing relative clauses).