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A superimposed code such as Zatocoding is a kind of hash code that is popular in marginal punched-card systems. == Marginal punched-card systems == (詳細はaperture card). Every card in a stack has the same set of pre-punched holes. The user finds the particular cards relevant to a search by aligning the holes in the set of cards (using a card holder or card tray), inserting one or more knitting-needle-like rods all the way through the stack, so the desired cards (which had been notched or cut open) fell out from the irrelevant cards in the collection (left un-notched), which remain on the needle(s). A user could repeat this selection many times to form a complex Boolean searching query. A card that was relevant to 2 or more subjects would have the slot(s) for each of those subjects cut out, so that card would drop out when either one or the other or both subjects was selected . The "superimposed code" coding systems, such as Zatocoding, saved space by entering several or all subjects in the same field; such a "superimposed code" stores much more information in less space, but at the cost of occasional "false" selections.〔 Robert V. Williams. ("Punched Cards: A Brief Tutorial" ). computing now 2002. 〕 Once you have a collection of index cards, one per book, research paper, or journal article in a library, with a list of keywords (subjects) discussed in a particular book written on that book's card, the "obvious way" to code those subjects is to count up the total number of subjects used in the entire collection R, make a row of R holes near the top of every card, and for each subject actually discussed in a particular book, cut a slot from the hole corresponding to that subject in the card corresponding to that book. 〔 W. Ross Ashby. (W. Ross Ashby's Journal: Zato-coding ) 1960 Sep. 22. p. 6208-6222 〕 Naturally, this also requires a separate list of every subject used in the collection that indicates which hole is punched for each subject. Unfortunately, there may be thousands of distinct subjects in the collection, and it is impractical to punch thousands of holes in every card. While it may not seem possible to use less than 1 hole per subject, superimposed code systems can solve this problem. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「superimposed code」の詳細全文を読む スポンサード リンク
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