The term schema refers to the overall design of the data Base. It is a logical database description and is drawn as
a chart of the type of data that are used it gives the
Name of the entity and relationship between them for example an Information display system that gives info about arrival and departure of train and aircraft at stations. The schema
will remain the same though the values displayed in the
system will change from time to time. The term subschema
refers to the same view but but for the data item types and
record types which are used in a particular application or
by particular user.
Schemas are generally stored in a data dictionary. Although a schema is defined in text database language, the term is often used to refer to a graphical depiction of the database structure
A database schema is a way to logically group objects such as tables, views, stored procedures etc. Think of a schema as a container of objects.
You can assign a user login permissions to a single schema so that the user can only access the objects they are authorized to access.
Schemas can be created and altered in a database, and users can be granted access to a schema. A schema can be owned by any user, and schema ownership is transferable.