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Relational Model . EF Codd proposed 12 RulesEFCoddRules.pptx

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Nukala Gopala Krishna Murthy
Nukala Gopala Krishna Murthy

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EF Codd Rules
EF Codd Rules Rule 0: The foundation rule: This rule states that for a system to qualify as an RDBMS, it must be able to manage database entirely through the relational capabilities. Rule 1: The information rule: All information(including metadata) is to be represented as stored data in cells of tables. Rule 2: The guaranteed access rule: Each unique piece of data(atomic value) should be accessible by : Table Name + Primary Key(Row) + Attribute(column).
EF Codd Rules Rule 3: Systematic treatment of null values: Null has several meanings, it can mean missing data, not applicable or no value. It should be handled consistently. Also, Primary key must not be null, ever. Expression on NULL must give null. Rule 4: Active Online Catlog: Database dictionary(catalog) is the structure description of the complete Database and it must be stored online. The Catalog must be governed by same rules as rest of the database. The same query language should be used on catalog as used to query database.
EF Codd Rules Rule 5: The comprehensive data sublanguage rule: One well structured language must be there to provide all manners of access to the data stored in the database. Example: SQL, etc. If the database allows access to the data without the use of this language, then that is a violation. Data definition. View definition. Data manipulation (interactive and by program). Integrity constraints. Authorization. Transaction boundaries (begin, commit and rollback). Rule 6: The view updating rule: All views that are theoretically updatable are also updatable by the system.
EF Codd Rules Rule 7: Relational level Operations Rule / Possible for high-level insert, update, and delete: There must be Insert, Delete, Update operations at each level of relations. Set operation like Union, Intersection and minus should also be supported. Rule 8: Physical data independence: The physical storage of data should not matter to the system. If say, some file supporting table is renamed or moved from one disk to another, it should not effect the application..
EF Codd Rules Rule 9: Logical data independence: Application programs and terminal activities remain logically unimpaired when information-preserving changes of any kind that theoretically permit un impairment are made to the base tables. If there is change in the logical structure(table structures) of the database the user view of data should not change. Rule 10: Integrity independence: Integrity constraints specific to a particular relational data base must be definable in the relational data sublanguage and storable in the catalog, not in the application programs.
EF Codd Rules Rule 11: Distribution independence: The end-user must not be able to see that the data is distributed over various locations. Users should always get the impression that the data is located at one site only. A database should work properly regardless of its distribution across a network. Even if a database is geographically distributed, with data stored in pieces, the end user should get an impression that it is stored at the same place. This lays the foundation of distributed database. Rule 12: Non subversion rule: If low level access is allowed to a system it should not be able to subvert or bypass integrity rules to change the data. This can be achieved by some sort of looking or encryption

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Relational Model . EF Codd proposed 12 RulesEFCoddRules.pptx

  • 2. EF Codd Rules Rule 0: The foundation rule: This rule states that for a system to qualify as an RDBMS, it must be able to manage database entirely through the relational capabilities. Rule 1: The information rule: All information(including metadata) is to be represented as stored data in cells of tables. Rule 2: The guaranteed access rule: Each unique piece of data(atomic value) should be accessible by : Table Name + Primary Key(Row) + Attribute(column).
  • 3. EF Codd Rules Rule 3: Systematic treatment of null values: Null has several meanings, it can mean missing data, not applicable or no value. It should be handled consistently. Also, Primary key must not be null, ever. Expression on NULL must give null. Rule 4: Active Online Catlog: Database dictionary(catalog) is the structure description of the complete Database and it must be stored online. The Catalog must be governed by same rules as rest of the database. The same query language should be used on catalog as used to query database.
  • 4. EF Codd Rules Rule 5: The comprehensive data sublanguage rule: One well structured language must be there to provide all manners of access to the data stored in the database. Example: SQL, etc. If the database allows access to the data without the use of this language, then that is a violation. Data definition. View definition. Data manipulation (interactive and by program). Integrity constraints. Authorization. Transaction boundaries (begin, commit and rollback). Rule 6: The view updating rule: All views that are theoretically updatable are also updatable by the system.
  • 5. EF Codd Rules Rule 7: Relational level Operations Rule / Possible for high-level insert, update, and delete: There must be Insert, Delete, Update operations at each level of relations. Set operation like Union, Intersection and minus should also be supported. Rule 8: Physical data independence: The physical storage of data should not matter to the system. If say, some file supporting table is renamed or moved from one disk to another, it should not effect the application..
  • 6. EF Codd Rules Rule 9: Logical data independence: Application programs and terminal activities remain logically unimpaired when information-preserving changes of any kind that theoretically permit un impairment are made to the base tables. If there is change in the logical structure(table structures) of the database the user view of data should not change. Rule 10: Integrity independence: Integrity constraints specific to a particular relational data base must be definable in the relational data sublanguage and storable in the catalog, not in the application programs.
  • 7. EF Codd Rules Rule 11: Distribution independence: The end-user must not be able to see that the data is distributed over various locations. Users should always get the impression that the data is located at one site only. A database should work properly regardless of its distribution across a network. Even if a database is geographically distributed, with data stored in pieces, the end user should get an impression that it is stored at the same place. This lays the foundation of distributed database. Rule 12: Non subversion rule: If low level access is allowed to a system it should not be able to subvert or bypass integrity rules to change the data. This can be achieved by some sort of looking or encryption