3-Level Architecture

The ANSI-SPARC three-level architecture is a foundational concept in database design that provides a framework for achieving data abstraction and independence. It divides a database system into three distinct levels. The lowest level is the Internal or Physical Level. This level is closest to the physical storage and describes how the data is actually stored on disk. It deals with low-level details like data structures (e.g., B+ trees, hash tables), file organization, storage allocation, and access paths (indexes). This level is primarily the concern of database developers and administrators. The middle level is the Conceptual or Logical Level. This level provides a unified, abstract view of the entire database. It describes what data is stored and the relationships between that data, without getting into the physical storage details. It defines all the entities, attributes, and relationships in a technology-agnostic way. The Database Administrator (DBA) works at this level to define the overall structure of the database. The highest level is the External or View Level. This level describes the part of the database that is relevant to a specific user or group of users. A database can have multiple external views. For example, in a university database, a view for students might only show course information, while a view for the finance department might only show fee details. This level provides a customized interface and enhances security by hiding irrelevant or sensitive data from certain users.