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:…to find gene families at the protein level using similarity search or protein motif databases, such as BLOCKS+ (Henikoff et al. 1999), Pfam (Bateman et al. 1999), ProDom (Corpet et al. 1999), PRINTS (Attwood et al. 1999), PROSITE (Hofmann et al. 1999), IntroPro (http:// www.ebi.ac.uk/interpro/).
Category: