The database schema is a structure or architecture to store data in the database. It creates abstraction(hide the lowest level the detail from the user) between application and physical database. A user creates a relationship with the help of Database Management System.But a user can’t see which type of data structure is used by the system to store the data in it.This data structure may be linear and may be non-linear, we don’t know. This is known as Abstraction. The database divided into three-level architecture is also known as three; schema architecture.
Database scheme is contained attributes and instructions to handle how data will be stored and how data related to each other and how can we access the data.
Three level architecture is used to obtain data isolation (Program data and program Operation remains independent), to support multiple users and use a perfect database structure to store data. This structure is also known as the ANSI/SPARC architecture.
Three level architecture divide the database into three level to create a separation between the user application and physical database. DBMS divide the whole process starting from creating a relation to accessing the content from the database. This three level separation is internal level, conceptual level, and Physical level. All these level represent different working purpose. Older DBMS include physical level detail at the conceptual level. ANSI/SPARC architecture important architecture of database to explain all three level separately.
Internal Level: Internal level is the last level among three level. It is also known as physical view level. It deals with data storage structure (B+ trees, Hash-table) and data access way to access the data in the least time from the database. B+ trees, Hash-table data structure, is used for storing data and Index table, primary key and foreign key constraints used for quick access or redundancy-free data. The user does not interact with this level.Primary key describes internal level, foreign key and index to access the data in the least time. This level is written in DDL language.
Conceptual Level: The Conceptual view is also known as a Logical level view. This level explains entire database.It hides all physical data storage detail from the user and focuses on relations, datatype, operations, and constraints. Database programmer and Database administrator work at this level for creating functions, triggers, procedure, relations in the table.
External View: External level is the highest level view. It is the closest interface to the user. With the help of GUI interface interact with the system without knowing which type of data stored and how the data stored in the database. User, group of users and unique user(DBA) deal with a view, to communicate with the database.