Of the 12 Edgar F. Codd formulated the basics of the relational design rules, which rule do you feel is the most importance when developing a database and explain why.

Rule 1 (The Foundation Rule) - Specifies that the system must qualify to be called as RDBMS and should utilize its relational capabilities to manage a database.

Rule 2 (The Information Rule) Specifies that all the information in a database must be represented as values in tables

Rule 3 (The guaranteed access rule) Specifies that every value in a database should be accessible by using a combination of table name, primary key and column name. This rule is to ensure that the data accessed is not ambiguous.

Rule 4 (Systematic treatment of NULL values) Specifies that an RDBMS must be capable enough to support a missing value, which is different from the regular values, such as zero or any other number. In addition, the missing value must be independent of any data type. In simple words, a RDBMS should support a field that can contain a NULL value (empty value).

Rule 5 (Active online catalog based on the relational model) Specifies that a RDBMS must support an online, inline, or relational catalog that the authorized users can access through their regular query language. In simple words, the catalog should be accessible to the users through the same query language that is used by them to access the database data.

Rule 6 (The comprehensive data sublanguage rule) Specifies that a RDBMS must support at least one relational language, which must include the following functionalities:-

Data definition operations, such as view definitions. Data manipulation operations, such as update and retrieval Transaction management operations, such as BEGIN, COMMIT and ROLLBACK. Security and integrity constraints.

Rule 7 (The view updating rule) Specifies that a view must support all data manipulation operations that are available to a table. Views are the data provided to the user in different logical combinations. In actual practice, it is very difficult to provide the update ad delete access to the logical views; and at present, such practice is not completely supported by any existing RDBMSs.

Rule 8 (The high-level insert, update and delete) Specifies that the data manipulation commands such as INSERT, UPDATE and DELETE can be executed on multiple rows and/or multiple tables rather than only on a single row of a single table.

Rule 9 (Physical Data independence) Specifies that the physical method of storing and retrieving information from the database should be kept hidden from the user. However, modifications to the physical methods should be allowed without affecting the way the users access the database. In other words, the application programs should remain unaffected if changes are made to either storage representations or access methods.

Rule 10 (Logical data independence) Specifies that the user view of data should not change when there is a change in the logical structure (table structure) of the database. In other words, the application programs and other activities must remain unaffected by a change in the logical structure of the database. This rule is very difficult to fulfill as in most of the RDBMSs, the user view of the data depends on the actual structure of the tables.

Rule 11 (Integrity independence) Specifies that the integrity constraints on the data entered by the user must be defined and stored separately from the application programs in a catalog. Whenever required, the RDBMS should allow modifying the constraints without affecting application programs.

Rule 12 (Distribution independence) Specifies that the application program should remain unaffected when data stored in a database is distributed or redistributed to multiple locations. In other words, the distribution of parts of a database to multiple locations should be hidden from the user. This rule is also very difficult to implement