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Chapter 23. Working with Databases > Relational Databases

Relational Databases

Although there are a number of database models, one of the most common and the one we will discuss is the relational database. The relational database model was introduced in 1970 by an IBM employee named E.F. Codd. Codd defined a relational database as a collection of data items organized as a set of defined tables from which data can be accessed and presented in different ways without having to reorganize the database tables. Although this initially sounds a bit confusing, the relational database model is actually fairly simple when viewed as a set of basic guidelines:

  • Relationships are represented by tables.

  • Each row represents a unique instance of an entity.

  • Columns are attributes of the entity.

  • Every table has an attribute or set of attributes that when combined form a “key” that uniquely identifies each entity.

  • Data is presented as a collection of relations; that is, users of the database could obtain a view of the database that fitted their needs.


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