▁file ▁system ▁that ▁displays ▁specific ▁versions ▁of ▁data ▁stored . ▁In ▁particular , ▁it ▁supports ▁dynamic ▁views ▁which ▁can ▁show ▁an ▁arbitrary ▁combination ▁of ▁local ▁and ▁remote ▁files . ▁ ▁History ▁▁ ▁Clear Case ▁was ▁developed ▁by ▁At ria ▁Software ▁and ▁first ▁released ▁in ▁ 1 9 9 2 ▁on ▁Unix ▁and ▁later ▁on ▁Windows . ▁Some ▁of ▁the ▁At ria ▁developers ▁had ▁worked ▁on ▁an ▁earlier , ▁similar ▁system : ▁D SEE ▁( Domain ▁Software ▁Engineering ▁Environment ) ▁from ▁Apol lo ▁Computer . ▁After ▁H ew lett - Pack ard ▁bought ▁Apol lo ▁Computer ▁in ▁ 1 9 8 9 , ▁those ▁developers ▁left ▁to ▁form ▁At ria . ▁At ria ▁later ▁merged ▁with ▁P ure ▁Software ▁to ▁form ▁P ure At ria . ▁That ▁firm ▁was ▁acquired ▁by ▁R ational ▁Software , ▁which ▁was ▁purchased ▁by ▁IBM ▁in ▁ 2 0 0 3 . ▁IBM ▁continues ▁to ▁develop ▁and ▁market ▁Clear Case . ▁In ▁September ▁ 2 0 1 6 , ▁IBM ▁announced ▁a ▁strateg ic ▁partners hip ▁with ▁H CL ▁Techn ologies ▁that ▁will ▁allow ▁for ▁acceler ated ▁development . ▁ ▁D SEE ▁introduced ▁many ▁concepts ▁that ▁were ▁adopted ▁by ▁Clear Case . ▁The ▁Apol lo ▁Domain ▁file ▁system ▁allowed ▁special ▁handler ▁programs ▁to ▁interven e ▁during ▁file ▁access . ▁D SEE ▁made ▁use ▁of ▁this ▁feature ▁to ▁in vis ibly ▁substitute ▁a ▁version ed ▁copy ▁when ▁a ▁particular ▁file ▁was ▁opened . ▁ ▁With ▁the ▁version ing ▁specification ▁resident ▁in ▁the ▁user ▁environment , ▁all ▁access es ▁to ▁version