Database System
Database Environment
, Objectives of Three-Level Architecture
• All users should be able to access the same data.
• The user's view cannot be changed.
• Users do not need to know the details of the database's physical storage.
• The DBA must be able to change the database storage structure without affecting the user
interface.
• The internal structure of the database must be unaffected by changes in the physical aspects
of the storage.
• The DBA must be able to change the conceptual structure of the database without affecting
all users.
Database System Architecture
External Level
▪ User's view of the Database.
▪ Describes how existing data is represented for different users.
The external level is the individual user level, where each user will only be interested in one
part. The view of each user is abstract compared to how the data is actually stored. Each user's
view is called an external view, which contains various types of external records. So this level is
closely related to the user, where each user only needs part of the data in the database. The
external view is only limited to the entities, attributes, and relationships between entities that
are needed
Conceptual Level
▪ Community view of the database.
▪ Describes what data is stored and the relationships between data.
Conceptual view is an overall information representation of the database contents, where all
the views of each user are combined. It is abstract, compared to how data is actually physically
stored. The conceptual view contains various types of conceptual records defined by the
conceptual schema, written in data definition language (DDL). Defining the conceptual schema
is intended to include additional features, such as security and integrity. Some of the main
objectives of the conceptual schema include; describing the complete enterprise, how the data
Database Environment
, Objectives of Three-Level Architecture
• All users should be able to access the same data.
• The user's view cannot be changed.
• Users do not need to know the details of the database's physical storage.
• The DBA must be able to change the database storage structure without affecting the user
interface.
• The internal structure of the database must be unaffected by changes in the physical aspects
of the storage.
• The DBA must be able to change the conceptual structure of the database without affecting
all users.
Database System Architecture
External Level
▪ User's view of the Database.
▪ Describes how existing data is represented for different users.
The external level is the individual user level, where each user will only be interested in one
part. The view of each user is abstract compared to how the data is actually stored. Each user's
view is called an external view, which contains various types of external records. So this level is
closely related to the user, where each user only needs part of the data in the database. The
external view is only limited to the entities, attributes, and relationships between entities that
are needed
Conceptual Level
▪ Community view of the database.
▪ Describes what data is stored and the relationships between data.
Conceptual view is an overall information representation of the database contents, where all
the views of each user are combined. It is abstract, compared to how data is actually physically
stored. The conceptual view contains various types of conceptual records defined by the
conceptual schema, written in data definition language (DDL). Defining the conceptual schema
is intended to include additional features, such as security and integrity. Some of the main
objectives of the conceptual schema include; describing the complete enterprise, how the data
