Edge-notched cards and relational databases

by Paul Curzon, Queen Mary University of London

An edge-notched card for Bob Marley and the Wailers notched as a Reggae Group with initials B-M-W: those three letters are notched, the other letters are un-notched.

Why not create an edge notched card system for something you are interested in, for identifying birds perhaps or quickly finding details of films, or music or of something you collect?

Edge-notched cards (see the Wood Computer) implement a physical, but still powerful, version of a database: an organised way of storing data. Information about some specific thing is represented on the card by cutting notches into holes around the edges following a set of codes.

Databases consist of lots of records each storing the information about one thing like one kind of timber. Each card in our pack corresponds to a record. A whole pack of records about one thing (like our pack of cards) is a database table. Records consist of fields with each field describing some aspect of the data like what the grain of the timber is like. Each group of related notches therefore acts as a database field.

In a relational database you do not have one gigantic set of records, so not just one gigantic pack of cards. You have a series of different sets of records/cards. Each has fewer fields so fewer holes as they no longer need to store details of every possible feature. Each smaller pack of cards is a table describing a specific thing (so if the cards store information about trees, the smaller packs might be about features of leaves and bark). There is also still a master pack describing trees as a whole. The tree cards no longer have to include all the details of leaves and bark, however. Instead each table includes a unique identifier field. Leaf cards include a leaf identifier that is also on the tree’s card. Bark cards similarly include a bark identifier. Once you have identified the leaf, you can use the leaf identifier on the tree cards to find any trees with that set of properties of leaf, then narrow it down further once you know the bark identifier. The smaller packs of cards still do the job but in a much more convenient way.

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This article was funded by UKRI, through Professor Ursula Martin’s grant EP/K040251/2 and grant EP/W033615/1.

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