Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:Thereafter, two groups reported the purification and characterization of 2,6-dihydroxybenzoate decarboxylases of Rhizobium radiobacter (formerly named as A. tumefaciens) WU-0108 (Ishii et al. 2004) and Rhizobium sp. strain MTP-10005 (Yoshida et al. 2004b) independently.
Category: