Relational Model

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The Relational Database Model
A database can be understood as a collection of related files. How those files are related depends on the model used. Early models included the hierarchical model (where files are related in a parent/child manner, with each child file having at most one parent file), and the network model (where files are related as owners and members, similar to the network model except that each member file can have more than one owner).

The relational database model was a huge step forward, as it allowed files to be related by means of a common field. In order to relate any two files, they simply need to have a common field, which makes the model extremely flexible.

Poet Code First Name Surname Age
1 Mongane Afrika 62
2 Stephen Serote 58
3 Tatumkhulu Watson 29

Poem Title Poet
Wakening Night 1
Thrones of Darkness 2
Once 3

These two tables relate through the code field in the poet table, and the poet field in the poem table. We can see who wrote the poem 'Once' by following the relationship, and see that it was poet 3, or Tatumkhulu Watson.

In 1970, when E.F. Codd developed the model, it was thought to be hopelessly impractical, as the machines of the time could not cope with the overhead necessary to maintain the model. Of course, hardware since then has come on in huge strides, so that today even the most basic of PC's can run sophisticated relational database management systems. Together with this went the development of SQL. SQL is relatively easy to learn and allows people to quickly learn how to perform queries on a relational database. This simplicity is part of the reason that relational databases now form the majority of databases to be found.

Basic Terms
An understanding of relational databases requires an understanding of some of the basic terms.

Data are the values stored in the database. On its own, data means very little. "43156" is an example.
Information is data that is processed to have a meaning. For example, "43156" is the population of the town of Littlewood.
A database is a collection of tables.
Each table contains records, which are the horizontal rows in the table. These are also called tuples.
Each record contains fields, which are the vertical columns of the table. These are also called attributes. An example would be a product record.
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