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Understanding the Three-Level Architecture in Database Management Systems

This lecture provides an overview of the Three-Level Architecture in Database Management Systems (DBMS), emphasizing the roles of various levels, including the external, conceptual, and internal levels. It highlights the importance of data independence, both logical and physical, allowing database administrators (DBAs) to change database storage structures and conceptual schemas without impacting user views or application programs. The lecture serves as a crucial resource for understanding how different components of a database interact and how they can be managed effectively.

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Understanding the Three-Level Architecture in Database Management Systems

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  1. DATABASE Management Systems Lecture 4

  2. Three-Level Architecture • DBA should be able to change database storage structures without affecting the users’ views. • Internal structure of database should be unaffected by changes to physical aspects of storage. • DBA should be able to change conceptual structure of database without affecting all users. Muhammad Tehseen Qureshi

  3. Three-Level Architecture Muhammad Tehseen Qureshi

  4. Three-Level Architecture • External Level • Users’ view of the database. • Describes that part of database that is relevant to a particular user. • Conceptual Level • Community view of the database. • Describes what data is stored in database and relationships among the data. Muhammad Tehseen Qureshi

  5. Three-Level Architecture • Internal Level • Physical representation of the database on the computer. • Describes how the data is stored in the database. Muhammad Tehseen Qureshi

  6. Data Independence • Logical Data Independence • Refers to immunity of external schemas to changes in conceptual schema. • Conceptual schema changes (e.g. addition/removal of entities). • Should not require changes to external schema or rewrites of application programs. Muhammad Tehseen Qureshi

  7. Data Independence • Physical Data Independence • Refers to immunity of conceptual schema to changes in the internal schema. • Internal schema changes (e.g. using different file organizations, storage structures/devices). • Should not require change to conceptual or external schemas. Muhammad Tehseen Qureshi

  8. Data Independence and the Three-Level Architecture Muhammad Tehseen Qureshi

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