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:Pellegrini-Calace M, Maiwald T, Thornton JM (2009) PoreWalker: A novel tool for the identification and characterization of channels in transmembrane proteins from their three-dimensional structure.
Category: