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4. Database Design Principles > 4.1. Redundancy

Redundancy

As we saw in Chapter 1, redundant data tends to inflate the size of a database, which can be a very serious problem for medium to large databases. Moreover, redundancy can lead to several types of anomalies, as discussed earlier. To understand the problems that can arise from redundancy, we need to take a closer look at what redundancy means.

Let us begin by observing that the attributes of a table scheme can be classified into three groups:

  • Attributes used strictly for identification purposes

  • Attributes used strictly for informational purposes

  • Attributes used for both identification and informational purposes

For example, consider the table scheme:

{PubID,PubName,PubPhone,YearFounded}

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