Understanding Relational Databases: Summary


Chapter Index

  1. Introduction
  2. Normalization
  3. Foreign Keys
  4. Denormalization
  5. Referential Integrity
  6. Summary

This is a free sample chapter from Beginning PHP 4 Databases published by Wrox Press.


In this chapter, we have discussed the principles behind relational database design. Let us skim through them here.

Data is stored in two-dimensional tables consisting of columns (fields) and rows (records). Multi-dimensional data is represented by a system of relationships among two-dimensional tables. This usually leads to data storage becoming redundant, and also difficult to maintain on account of addition and deletion anomalies. This is only the case if we do not normalize the data.

Normalization is a process by which redundancy and inconsistency are reduced or eliminated from a database’s schema. Denormalization is generally undesirable but sometimes necessary for performance reasons. Keys are fields or combinations of fields used to identify records. We also saw how entity relationship diagrams are used to map out the design of a database before it is built.

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