A fundamental feature of the database approach is that the database system does not
only contain the data but also the complete definition and description of these data.
These descriptions are basically details about the extent, the structure, the type
and the format of all data and, additionally, the relationship between the data. This
kind of stored data is called metadata ("data about data").
Metadata is used by the DBMS software but also by applications like GIS and by users of databases.
As DBMS software is not written for one specific database application the
metadata of a database is used to get information about the extent, the structure, etc. of
it.
Following is a simple example how data can be described in a database.
Following is a simple example how data can be described in a database.
Below there is a database table. Because of the structure of this table (first
column = Forename, second column = Surname, third column = Postcode, forth column
= City) it is known that a entry in the first column must be a forename (coded as
string) and an entry in the third column must be a postcode (coded as number).