ed ▁files ▁were ▁redirect ed , ▁including ▁such ▁m und ane ▁access es ▁as ▁printing , ▁view ing ▁in ▁a ▁generic ▁text ▁editor ▁etc . ▁ ▁D SEE ▁re lied ▁heavily ▁on ▁a ▁file ▁that ▁described ▁all ▁the ▁software ▁modules ▁and ▁their ▁dependencies . ▁The ▁file ▁had ▁to ▁be ▁generated ▁manually , ▁which ▁was ▁a ▁major ▁imped iment ▁to ▁its ▁use ▁in ▁large ▁systems . ▁However , ▁once ▁generated , ▁it ▁enabled ▁D SEE ▁to ▁calculate ▁the ▁optim um ▁way ▁to ▁perform ▁a ▁build , ▁re - using ▁all ▁modules ▁that ▁had ▁previously ▁been ▁processed ▁and ▁whose ▁version ▁specific ations ▁matched ▁the ▁specific ations ▁for ▁the ▁build . ▁ ▁D SEE ▁also ▁introduced ▁the ▁" version ▁spec ," ▁which ▁was ▁called ▁a ▁" thread ." ▁This ▁was ▁a ▁list ▁of ▁possible ▁versions ▁that ▁could ▁be ▁in ▁the ▁user ▁environment ▁or ▁in ▁a ▁build . ▁A ▁major ▁innov ation ▁was ▁the ▁use ▁of ▁build ▁sign atures ▁and ▁software ▁release ▁sign atures ▁in ▁the ▁thread . ▁The ▁items ▁in ▁a ▁thread ▁might ▁thus ▁be : ▁ ▁Any ▁copies ▁reserved ▁for ▁editing ▁( i . e . ▁checked ▁out ) ▁ ▁The ▁latest ▁version ▁( us ually ▁for ▁developers ▁only ) ▁ ▁A ▁branch ed ▁version ▁of ▁a ▁file ▁( a ▁version ▁on ▁an ▁alternate ▁line ▁of ▁development ). ▁ ▁A ▁l abeled ▁version ▁( for ▁developers ▁working ▁on ▁a ▁particular ▁revision ▁level ) ▁ ▁The ▁version ▁used ▁in ▁build ▁X Y Z . ▁ ▁The ▁version ▁used ▁in ▁software ▁release ▁x . y . z