an Entity references as follows:
S.T.A.L.K.E.R.: Clear Sky is a 2008 first-person shooter survival horror video game with role-playing elements. It was developed by GSC Game World and published by Deep Silver as a prequel to S.T.A.L.K.E.R.: Shadow of Chernobyl. A third game, S.T.A.L.K.E.R.: Call of Pripyat was released in 2009 as a sequel to Shadow of Chernobyl.