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DATABASE Management Systems

DATABASE Management Systems. Lecture 4. 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.

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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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