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:Several models for provenance have emerged to tackle this vision, including Provenir [20, 21], the Provenance Vocabulary [22], PASOA [23], OPMV [24], PML [25] and the Open Provenance Model [26].
Category: