Purpose - As the virtual reference service (VRS) is becoming a standard service of the digital library, efficient collaboration among virtual reference services is also becoming more and more important for information exchange and sharing. This paper seeks to examine existing collaborative VRS systems with a view to achieving collaboration. Design/methodology/approach - This paper studies existing collaborative VRS (CVRS) systems and analyzes their structures, methods and functions for achieving collaboration. Findings - Three collaborative structure models are proposed and basic collaborative methods and collaborative functions are concluded. A CVRS reference model is depicted. Research limitations/implications - Since the study is not based on an exhaustive list of CVRS systems and technologies are always developing, the collaborative structure models, methods and functions presented in this paper are possibly not complete and may need to be adjusted and amended. There is also urgent work to be done to advance and establish related standards and protocols for CVRS. Practical implications - The study is intended to help libraries to identify quickly the necessary elements and mechanisms for the design of a proper degree of CVRS or to develop or evaluate VRS systems. Originality/value - This paper proposes and concludes collaborative structure models, methods, functions and a reference model of URS. It should prove helpful for libraries wishing to provide CVRS, as well as for further research on CVRS.
