Dr E.F. Codd an IBM researcher , first developed the relational data model in 1970 . In 1965 , Dr Codd published a list of 12 rules that concisely define an ideal relational database , which have provided a guideline for the design of all relational database systems ever since.
Following are the lists of CODD's 12 rules.
1.The Information Rule :
All data should be presented to the user in table form .
2.Guaranteed Access Rule :
All data should be accessible without ambiguity . This can be accomplished through a combination of the table name , primary key and column name.
3.Systematic Treatment of Null Values :
A field should be allowed to remain empty . This involves the support of null value which is distinct from empty string or a number with a value of zero . Of course , this can't apply to primary keys . In addition , most database implementations support the concept of a non - null field constraints that prevents null values in a specific table column.
4.Dynamic On-Line Catalog Based on the Relational Model :
A relational database must provide access to its structure through the same tools that are used to access the data . This is usually accomplished by storing the structure definition within special system tables.
5.Comprehensive Data Sublanguage Rule :
The database must support a
6.View Updating Rule :
7.High-level Insert , Update and Delete :
8.Physical Data Independence :
9.Logical Data Independence :
10.Integrity Independence :
11.Distribution Independence :
12.No Subversion Rule :
Following are the lists of CODD's 12 rules.
1.The Information Rule :
All data should be presented to the user in table form .
2.Guaranteed Access Rule :
All data should be accessible without ambiguity . This can be accomplished through a combination of the table name , primary key and column name.
3.Systematic Treatment of Null Values :
A field should be allowed to remain empty . This involves the support of null value which is distinct from empty string or a number with a value of zero . Of course , this can't apply to primary keys . In addition , most database implementations support the concept of a non - null field constraints that prevents null values in a specific table column.
4.Dynamic On-Line Catalog Based on the Relational Model :
A relational database must provide access to its structure through the same tools that are used to access the data . This is usually accomplished by storing the structure definition within special system tables.
5.Comprehensive Data Sublanguage Rule :
The database must support a
6.View Updating Rule :
7.High-level Insert , Update and Delete :
8.Physical Data Independence :
9.Logical Data Independence :
10.Integrity Independence :
11.Distribution Independence :
12.No Subversion Rule :
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