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Database Management System rules and protocols by E.F. (Edger Frank) Codd or EF CODD's Rules

Edger Frank aka E.F. Codd suggested some rules to follow while implementing a relational DBMS. He suggested that a relational database should follow the following rules so that it would work functionally efficient and it will also avoid the unnecessary background operation of the system.
Database Management System rules and protocols by E.F. (Edger Frank) Codd or EF CODD's Rules: 
  1. Information Rule : A set of related tables forms a database and all data is represented as tables, the data can be viewed in no other ways.
  2. Guaranteed Access : Each value can be accessed by specifying tables name, primary key 7 column name. This way each & every value is uniquely identifiable & accessible. Basically its a restatement of the fundamental requirement for primary keys.Each piece of data must be logically accessible by referencing A Table, A Primary/Unique Key and A Column.
  3. Systematic Treatment of Null Values : Null must be always be interpreted as an unknown value. 
  4. Dynamic online catalog based on the relational model. A relational database contains data about itself. There are two types of tables in a RDBMS. User Table : Containing the working data / actual data. System Table : contain data about the data structure of the user tables or meta data to control the user tables. Meta Data is data that describes the structure of the database itself and includes object definition (Tables, Indexes, stored procedure etc. And how they related to each other.). The collection of system tables is also referred as the system catalog or data dictionary. 
  5. Comprehensive Data Sub Language : SQL is the de-facto of standard or a relational database language. SQL is a non procedural or declarative language, it allows users to express what they want from a RDBMS with out specifying the details about where it is located or how to get it, user just need to focus on what is want to get.
  6. View Updating Rule : A relational database must not be limited to source tables when presenting data to the user. Data can be presented to the user in different logical combinations called as Views. Views are virtual tables or abstractions to the source tables.Views allows the creation of custom tables that are tailored for a specific need.
  7. High Level INSERT, UPDATE, DELETE : Rows are treated as sets for data manipulation operations like INSERT, UPDATE, DELETE. (SELECT is not a DML command). A relational database must support basic relational algebra operations (Selection, Projections and Joins) and Set operations (Union, Intersection, Division, Difference). A database that supports only row at a time (navigational) operations, doesn't meet this requirement and is not considered as relational database.
  8. Physical Data Independence : Application that access data in a relational database must be unaffected by changes in the way the data is physically stored.
  9. Logical Data Independence : The database schema or structure of tables and relationships can change with out having to recreate the application that uses it.
  10. Integrity Independence : Data integrity means the consistency & accuracy of the data in the database i.e. Keeping the garbage out of the database. In order to be considered relational data integrity must be an internal functionality of the database, not of the application program.
  11. Distribution Independence : The data manipulation language of the RDBMS should be able to work with distributed database. Views should be able to join data from tables on different servers as well as from different RDBMS. The user should not have to aware of whether a database is distributed or not it should support all the operations perform by the users.
  12. Non Sub-version Rule : There can't be other paths into database that subvert data integrity. In other words, you can't get in the “BACKDOOR” & change the data in such a manner as data integrity is violated.

So these are the rules/protocols are suggested by E.F. Codd to implement a relational database. These are the points keep into mind while designing a RDBMS.
From the database developer perspective we need to focus on the below points:
  1. No two tuples should have same data.
  2. Key : set of minimum attributes used to differentiate all tuples is known as key.
  3. Key can be simple i.e. Having only one attribute that can differentiate all the tuples e.g. Email-address of the user in user table, Enrollment No in Student table etc.
  4. Key can be composite or compound i.e. Having multiple attributes need to differentiate all the tuples e.g. Name, Father Name, Class/Section and City  in the student table.

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