JNTU B.Tech III DATABASE MANAGEMENT SYSTEMS Previous Question Paper (September - 2021 - R16)

The DBMS system architecture is commonly described using the ANSI-SPARC three-level architecture, which aims to achieve data independence by separating the user's view from the physical storage of data.

1. External Level (View Level): This is the highest level, consisting of multiple external schemas or user views. Each view describes only a part of the database relevant to a specific user group, hiding the rest of the database for security and simplicity.
2. Conceptual Level (Logical Level): This level represents the entire database structure. It describes what data is stored, the relationships between data entities, and the constraints (integrity rules) applied. It acts as a bridge between the physical and external levels.
3. Internal Level (Physical Level): This is the lowest level, describing how data is actually stored on the storage media. It deals with file organizations, indexing techniques, and data compression, focusing on performance and storage efficiency.

This architecture supports Data Independence: Logical data independence allows changes to the conceptual schema without affecting external views, while physical data independence allows changes to the internal storage structure without affecting the conceptual schema.

A Schema is the overall logical description or blueprint of a database. It defines the structure of the database, including the tables, fields, data types, and the relationships between them. A schema is typically defined during the database design phase and does not change frequently. It provides the framework within which data is stored.

A View is a virtual table that does not exist physically in the database. It is derived from one or more base tables using a query. Views are used to provide a customized perspective of the data to different users. Key characteristics include:

• Security: Users can be granted access to a view rather than the underlying base tables, restricting their access to sensitive columns or rows.
• Simplicity: Complex queries involving multiple joins can be stored as a view, allowing users to query the view as if it were a simple table.
• Dynamic Nature: Since a view is a stored query, it always reflects the current data present in the base tables.