Dr. Edgar F. Codd, after his extensive research on the Relational Model of database systems, came up with twelve rules of his own, which according to him, a database must obey in order to be regarded as a true relational database.

These rules can be applied on any database system that manages stored data using only its relational capabilities. This is a foundation rule, which acts as a base for all the other rules.

Rule 1: Information Rule

The information put away in a database, might it be client information or metadata, must be an estimation of some table cell. Everything in a database must be put away in a table configuration.

Rule 2: Guaranteed Access Rule

Each and every information component (quality) is ensured to be open legitimately with a blend of table-name, essential key (line esteem), and trait name (section esteem). No different means, for example, pointers, can be utilized to get to information

Rule 3: Systematic Treatment of NULL Values

The NULL qualities in a database must be given an orderly and uniform treatment. This is a vital guideline in light of the fact that a NULL can be translated as one the accompanying − information is missing, information is not known, or information is not pertinent.

Rule 4: Active Online Catalog

The structure depiction of the whole database must be put away in an online inventory, known as information lexicon, which can be gotten to by approved clients. Clients can utilize the same question dialect to get to the index which they use to get to the database itself.

Rule 5: Comprehensive Data Sub-Language

A database must be gotten to utilizing a dialect having straight punctuation that backings information definition, information control, and exchange administration operations. This dialect can be utilized specifically or by method for some application. On the off chance that the database permits access to information with no assistance of this dialect, then it is considered as an infringement.

Rule 6: View Updating Rule

Every one of the perspectives of a database, which can hypothetically be upgraded, should likewise be updatable by the framework.

Rule 7: High-Level Insert, Update, and Delete Rule

A database must bolster abnormal state insertion, updation, and erasure. This must not be restricted to a solitary column, that is, it should likewise bolster union, crossing point and short operations to yield sets of information records.

Rule 8: Physical Data Independence

The information put away in a database must be free of the applications that get to the database. Any adjustment in the physical structure of a database must not have any effect on how the information is being gotten to by outer applications.

Rule 9: Logical Data Independence

The consistent information in a database must be autonomous of its client’s perspective (application). Any change in coherent information must not influence the applications utilizing it. For instance, if two tables are consolidated or one is part into two unique tables, there ought to be no effect or change on the client application. This is a standout amongst the most troublesome tenet to apply.

Rule 10: Integrity Independence

A database must be free of the application that uses it. All its uprightness requirements can be freely altered without the need of any adjustment in the application. This tenet makes a database free of the front-end application and its interface.

Rule 11: Distribution Independence

The end-client must not have the capacity to see that the information is circulated over different areas. Clients ought to dependably get the feeling that the information is situated at one site as it were. This principle has been viewed as the establishment of appropriated database frameworks.

Rule 12: Non-Subversion Rule

On the off chance that a framework has an interface that gives access to low-level records, then the interface must not have the capacity to subvert the framework and detour security and honesty imperatives.

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