Codd's Twelve Rules - Rule 6 - View Updating Rule

Codd's Twelve Rules - Rule 6 - View Updating Rule

Rule 6	View Updating Rule
Rule	All views that are theoretically updateable are also updateable by the system.
Description	This rule deals with views, which are virtual tables used to give various users of a database different views of its structure. It’s one of the most challenging rules to implement in practice, and no commercial product fully satisfies it today. A view is theoretically updateable as long as it’s made up of columns that directly correspond to real table columns.
Example	All views are not updateable. Views can be updateable if they follow the certain rules unlike tables. The following syntax can be used to update views; UPDATE < view_name > SET<column1>=<value1>,<column2>=<value2>,..... WHERE <condition>;
Some DBMS that fulfills this property	SQL Server technically fulfills this rule by using INSTEAD OF triggers, MySQL support view update in some cases. For a view to be updatable, there must be a one-to-one relationship between the rows in the view and the rows in the underlying table in MySQL, All views that are theoretically updateable are also updateable by the Oracle system.

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Codd's Twelve Rules

Codd's Twelve Rules / Codd's Twelve Commandments / Relational Model Foundation Principles

Can we say “any database that supports SQL is a relational database”? No. At least, not completely. We need certain foundation principle to make this assessment. For any system to be called a relational database management system, the relational capabilities must be able to manage it completely. Edgar F. Codd, a pioneer of the relational model for databases, designed Codd’s twelve rules to define what is required from a database management system in order for it to be considered relational, i.e., a relational database management system (RDBMS).

Those rules are listed below and the links will lead you to the description pages of those rules.

Codd’s twelve rules

• Rule 1  : Information Rule

• Rule 2 : Guaranteed Access Rule

• Rule 3 : Systematic treatment of NULL values

• Rule 4 : Dynamic Online Catalog Based on the RelationalModel

• Rule 5 : Comprehensive Data Sublanguage Rule

• Rule 6 : View Updating Rule

• Rule 7 : High level Insert, Update, and Delete

• Rule 8 : Physical Data Independence

• Rule 9 : Logical Data Independence

• Rule 10: Integrity Independence

• Rule 11: Distribution Independence          

• Rule 12: Non-Subversion Rule