A DBMS can become a relational data base management system if it satisfies the Codd’s rules. There are 13 rules that should be satisfied for a DBMS to become RDBMS. Codd was a pioneer for relational model and he framed these rules so that no vendor dilutes the features of a relational database management system.

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The first rule states that a RDBMS must use relations exclusively to manage the database and second states that information should be represented in columns and that should be the only way of representing the information. The third rule states that all data should be accessible in the database when they are referred by the table name, column name and by using the primary keys.

The fourth rule is about the treatment of null values. It states that columns should be allowed for null values. The fifth rule states that the data structure also should be accessible through the same query language that is used to access data. The sixth is a sublanguage rule which states that at least one relational language must be supported which uses linear syntax, and interactively with the applications and also supports data definition, transactions, security and integrity operations.

Capability to update all views is the seventh Codd’s rule. The eighth rule is about high-level insert, update, and delete of data. It should be possible to do these in set of rows and not in singles. The next rule is that the data stored at the physical level, in the form of linked lists or arrays should not be changed based on the structure of the application. The next is about logical data independence. The other rules state about integrity independence and distribution independence. The final rule is about any bypass to the relational security of integrity constraint should not be provided by the low-level interface of the system.

If these Codd’s rules are followed in an DBMS then it qualifies to become a relational database management system.