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:The GHMP kinases which in 1993 firstly identified by protein sequence alignment in the form of sugar kinase (Bork et al. 1993; Timson 2007) are a structurally related family named after four of its members, galactokinase (EC 2.
Category: