DATA BASES

A relational database is a collection of data  items organized in relations as a set of  tables from which data can be accessed or reassembled in many different ways without having to reorganize the database tables. 

 

 

Each table is composed of a set of records and each one is identified by attributes called fields, which contain a unique value. Because of how fields are organized in a table users can access the data in almost unlimited number of ways. 

Database is  used to store lots of information. It enables a quick and very easy  access to information. It's also very easy to add new information  or delete old one. In addition one person can access it at the same like, which means it is multi-access.

Specific information is stored depending on the database's intended use. For example, the police have details of all known criminals in a database (all the crimes they've comitted). When trying to solve a crime they use the database to investigate possible criminals. 

Relational database has two specific types of keys:

• Primary key: it exists just one particular record for each field in a table. It can´t be repeated.
• Foreign key:it can relate different types of records by just one table