Codd's Twelve Rules - Rule 8 - Physical Data Independence

Codd's Twelve Rules - Rule 8 - Physical Data Independence

Rule 8	Physical Data Independence
Rule	Changes in the physical level must not lead to a change in the next higher level called logical level.
Description	Any change in the physical level (lowest level that talks about how data is stored in a database, say for example, in arrays or linked lists etc.) must not lead to a change in the logical level (tables, columns, rows etc.). Applications that are defined on the physical level should be able to continue to work even when changes are made to the internal implementation of data storage and access methods. The way the data stored physically must be independent of how its accessed logically.
Example	For example, relations are stored as unordered files. If the change from unordered files to some other representation would not require a change in the table design, attribute types etc.
Some DBMS that fulfills this property	Almost all Relational DBMSs support this property.

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Codd's Twelve Rules - Rule 1 - Information Rule

Codd's Twelve Rules / Rule 1 - Information Rule

Rule 1	Information Rule
Rule	All information in the relational database is represented in exactly one and only one way — by values in tables.
Description	Every piece of data/information that we store in a database permanently is in tables only. We will not be able to store in any other component other than tables.
Example	Emp_ID EName E101 Kumar E102 Virat E105 Sachin E103 Gurucharan E110 Kumar Sample table Employee is given above. Here, the record of every employee is stored in the table only.
Some DBMS that fulfills this property:	SQL Server, Oracle, and MySQL support tables with rows and columns.

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Codd's Twelve Rules - Rule 2 - Guaranteed Access Rule

Codd's Twelve Rules - Rule 2 - Guaranteed Access Rule

Rule 2	Guaranteed Access Rule
Rule	Each and every datum (atomic value) is guaranteed to be logically accessible by resorting to a combination of table name, primary key value, and column name.
Description	We must be able to access every single piece of information from the tables in some way. The combination “Table name + Primary key + Column name” must let us find the information what we need. In the case of multiple records in the result, the combination of “Table name + Column name” or the “Table name + * “ would find what we need.
Example	SELECT Emp_Salary FROM Employee WHERE ENo = ‘101’;           where, Employee is table name, Emp_Salary is required field, and ENo is the primary key.
Some DBMS that fulfills this property	SQL in Oracle, Transact SQL in SQL Server, and SQL in MySQL supports primary keys, and are able to access the data as said above.

 

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