ypes ▁are ▁not ▁so ▁clean ly ▁distinguished ▁in ▁software ▁and ▁systems ▁engineering , ▁where ▁mock ups ▁are ▁a ▁way ▁of ▁design ing ▁user ▁interfaces ▁on ▁paper ▁or ▁in ▁computer ▁images . ▁A ▁software ▁mock up ▁will ▁thus ▁look ▁like ▁the ▁real ▁thing , ▁but ▁will ▁not ▁do ▁useful ▁work ▁beyond ▁what ▁the ▁user ▁sees . ▁A ▁software ▁prototype , ▁on ▁the ▁other ▁hand , ▁will ▁look ▁and ▁work ▁just ▁like ▁the ▁real ▁thing . ▁In ▁many ▁cases ▁it ▁is ▁best ▁to ▁design ▁or ▁prototype ▁the ▁user ▁interface ▁before ▁source ▁code ▁is ▁written ▁or ▁hardware ▁is ▁built , ▁to ▁avoid ▁having ▁to ▁go ▁back ▁and ▁make ▁expensive ▁changes . ▁ ▁Early ▁layout s ▁of ▁a ▁World ▁W ide ▁Web ▁site ▁or ▁pages ▁are ▁often ▁called ▁mock ups . ▁A ▁large ▁selection ▁of ▁propriet ary ▁or ▁open - source ▁software ▁tools ▁are ▁available ▁for ▁this ▁purpose . ▁ ▁Military ▁ac quisition ▁ ▁Mock ups ▁are ▁part ▁of ▁the ▁military ▁ac quisition ▁process . ▁ ▁Mock ups ▁are ▁often ▁used ▁to ▁test ▁human ▁factors ▁and ▁aer od ynam ics , ▁for ▁example . ▁ ▁In ▁this ▁context , ▁mock ups ▁include ▁wire - frame ▁models . ▁They ▁can ▁also ▁be ▁used ▁for ▁public ▁display ▁and ▁demonstr ation ▁purposes ▁prior ▁to ▁the ▁development ▁of ▁a ▁prototype , ▁as ▁with ▁the ▁case ▁of ▁the ▁Lock he ed ▁Martin ▁F - 3 5 ▁Light ning ▁II ▁mock - up ▁aircraft . ▁ ▁Cons umer ▁goods ▁Mock ups ▁are ▁used ▁in ▁the ▁consumer ▁goods ▁industry ▁as ▁part ▁of ▁the ▁product