Brian Solis (2010). “Engage: The Complete Guide for Brands and Businesses to Build, Cultivate, and Measure Success in the New Web”, p.37, John Wiley & Sons
Brian Solis (2011). “Engage!, Revised and Updated: The Complete Guide for Brands and Businesses to Build, Cultivate, and Measure Success in the New Web”, p.3, John Wiley & Sons