Schema (A3.2 Database design)

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6 Terms

1
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Schema

Architecture showing how data is organized and how relationship between data is managed = logical view of database

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I. Types

Types of schema

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Conceptual schema (I)

Describes structure w/o considering how physically implemented

  • High-level representation defining structure and organization

    • Defines: entities, attributes, relationships

  • Abstract model that hides details (implementation of data structures, physical storage)

  • Most vague

<p><span style="background-color: transparent;"><span>Describes structure w/o considering how physically implemented</span></span></p><ul><li><p><span style="background-color: transparent;"><span>High-level representation defining structure and organization</span></span></p><ul><li><p><span style="background-color: transparent;"><span>Defines: entities, attributes, relationships</span></span></p></li></ul></li><li><p><span style="background-color: transparent;"><span>Abstract model that hides details (implementation of data structures, physical storage)</span></span></p></li><li><p><span style="background-color: transparent;"><span>Most vague</span></span></p></li></ul><p></p>
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Logical schema (I)

Design of structures of table (field, datatypes) and relationships 

  • Defines structure, attributes, fields, data types etc

  • Doesn’t consider requirement of specific DBMS

<p><span style="background-color: transparent;"><span>Design of structures of table (field, datatypes) and relationships&nbsp;</span></span></p><ul><li><p><span style="background-color: transparent;"><span>Defines structure, attributes, fields, data types etc</span></span></p></li><li><p><span style="background-color: transparent;"><span>Doesn’t consider requirement of specific DBMS</span></span></p></li></ul><p></p>
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Physical schema

Implementation of logical schema in specific DBMS = show how data is stored, indexed, accessed

  • THE actual db

  • Includes: specifics of storage devices, access methods, indexing, partitioning, access methods, views, configuration of db on storage media

  • Translates logical schema → implementation fitting requirements of specific DBMS

  • When write queries to create physical DB

<p><span style="background-color: transparent;"><span>Implementation of logical schema in specific DBMS = show how data is stored, indexed, accessed</span></span></p><ul><li><p><span style="background-color: transparent;"><span>THE actual db</span></span></p></li><li><p><span style="background-color: transparent;"><span>Includes: specifics of storage devices, access methods, indexing, partitioning, access methods, views, configuration of db on storage media</span></span></p></li><li><p><span style="background-color: transparent;"><span>Translates logical schema → implementation fitting requirements of specific DBMS</span></span></p></li><li><p><span style="background-color: transparent;"><span>When write queries to create physical DB</span></span></p></li></ul><p></p>
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II. Uses of schemas

  • Data organization: clear structure

  • Data security: defines user permissions and views

  • Data integrity: rules and constraints to maintain data accuracy and consistency

  • Performance: through use of queries

  • Scalability: allows for changes to DB w/o disrupting current applications