# Elementary data organization

Data are simply values or set of values. A single unit of values is called a Data item. Data items are divided into subgroups called Group items.

An Entity is something that has certain attributes which may be assigned values. An entity with similar attributes are called an Entity set.

Eg:-
Entity : Employee
Attribute : Name , Age phone
Values : "ABC", 42, 9847092568
Entity set : All employees in an organization.

Meaningful or processed data is called information.
Collection of data organized into the hierarchy of fields, records and files.
A single elementary unit of information representing an attribute of an entity is called a Field.

Records are the collection of field values of a given entity.
Collection of records of the entities in a given entity set is called a file.
Each record may contain a certain field that uniquely represents that record. Such a field K is called a Primary key.

Based on their length, records may be classified into two. They are,

Fixed length record : All record contain the same data items with the same amount of space assigned to each items.
Variance length record: Records may contain different length data items.