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:Large (23 S-like) and small (16 S-like) ribosomal subunit RNA sequences were obtained from the Antwerp database and the Ribosomal Database Project (Maidak et al., 1997; van de Peer et al., 1997a,b).
Category: