Relational databases store data in tables (relations) that are two
dimensional. The tables have rows (records or objects) and columns (fields
or attributes). Data items at an intersection of a row and a column are
called a cell and consist of attribute values. Data stored is simple data
such as integers, real numbers or string values. Multiple values may not
be stored in one cell. Relational database tables are "normalized" so data
is not repeated more often than necessary. All table columns depend on a
primary key (a unique value in the column) to identify the column. Once
the specific column is identified, data from one or more rows associated
with that column may be obtained or changed.
Relational databases are sets of tables. One table file is not a
relational database. A relational database server is not the same as a
relational database. A relational database can be a file with sets of
tables. The relational database server includes the ability to service
requests to get or change data from remote clients.
Relational database servers use Structured Query Language (SQL), as a
data manipulation language to interface between itself and the clients.
SQL is the standard for getting and storing data in an RDBMS.
Relational database servers provide:
- Data Management
- Transaction processing
- Data integrity - Provides for multiple access at the same time
(concurrency) between multiple processes/users. This is done so data is
not displayed nor saved in a fashion where one change is lost. Various
locking mechanisms are used to support this.
- Data backup and recovery.
- Data security - Provides for user authentication, and levels of data
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