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Statistical gymnastics - and fast

Everything you wanted to know about computers without showing your ignorance. Arnold Evans shows you the basics.

Imagine a database as a vast electronic filing cabinet - and you'd only be half wrong. The contents of a paper filing system can only be held in one pre-determined order - usually alphabetically. A database can be re-arranged in virtually any order you care to devise.

This is because each piece of information can be found instantly. For example, when the school roll is on a database, you can view the names in alphabetical order. But the database will happily re-arrange them in year groups. Or by date of birth. Or postal code. Or IQ score. Or any other "field" of information the files contain.

But you ain't seen nothing yet. You can ask the database to search for those names that meet two or more selection criteria. So you could ask it for "Boys, over 12 years-old, who do French on Tuesdays but do not stay for school lunch." (It's the sort of info the Department for Education and Employment is always wanting to know.) The computer will instantly provide the relevant files. The school administrators will have a field day with such information; it opens up new avenues when it comes to thinking about the curriculum, patterns of absenteeism, equal opportunities etc.

The faculty head could find a database equally useful. If the contents of course books are dutifully logged, for example, the geographer shouldn't have any trouble tracking down that colour picture of Etna erupting he vaguely remembers. The English department can record which books it has in stock, and which classes have already used them.

However, when consulting a database, it's worth remembering: "Rubbish in, rubbish out". If you don't feed the information in (input it) accurately and then regularly update it, the results can be positively misleading.

Children love compiling their own databases. They might do one on their class, pumping in physical characteristics and multifarious tastes and interests. A couple of key strokes, and they can then find all the Arsenal fans who are left- handed. It would, of course, be quicker to race round the classroom asking everyone - and that highlights the big problem with a database: it does take forever to pump in enough facts to make it worthwhile bothering with.

Fortunately, the commercial suppliers are more than happy to sell you as much digitised data as you want. It ranges from simple collections of facts about animals to government census returns.

Databases aren't limited to text. You can buy various collections of pictures, photographs and drawings. You can also stock a database with artwork that you have created yourself. But in order to create it, you will need a graphics package.

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