Chapter 16: The Basic Relational Model

Chapter 16: The Basic Relational Model

Overview

Like most new ideas, the hard part of understanding what the relational model is comes in unlearning what you know about file systems. Artemus Ward (William Graham Sumner, 1840?1910) put it very nicely: ?It ain?t what you don?t know that kills you; it?s what you know that ain?t so that kills you.?

If you already have a background in data processing with traditional file systems, the first things to unlearn are


	1.	Databases are not file sets.


	2.	Tables are not files.


	3.	Rows are not records.


	4.	Columns are not fields.

Do not feel ashamed of getting stuck in a conceptual rut; every new technology has this problem.

The U.S. standard railroad gauge (distance between the rails) is 4 feet, 8.5 inches. This gauge is used because the English built railroads to that gauge, and U.S. railroads were built by English expatriates.

Why did the English build railroads to that gauge? Because the first rail lines were built by the same people who built the prerailroad tramways, and that?s the gauge they used. Why did those wheelwrights use that gauge then? Because the people who built the horse-drawn trams used the same jigs and tools that they used for building wagons, which used that wheel spacing.

Why did the wagons use that odd wheel spacing? For the practical reason that any other spacing would break an axle on some of the old, long-distance roads, because this is...

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Chapter 16: The Basic Relational Model

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