Rules of RDBMS
In this session we discuss about the Codd’s rules. For any RDBMS to be accepted as a full- fledged Relational Data Base Management System, it has to follow the twelve rules of Codd’s. There are a number of products known as RDBMSs attempting to meet all twelve rules of Codd’s, but all the twelve rules are until now, not been satisfied through any RDBMS. Oracle is also, not 100 percent relational because it does not obey all Codd’s rules.
Codd’s Rules
Dr. E.F. Codd designed twelve rules for a database to be ready to use. The rules are listed as follows:
Information Rule
All the information in a relational database must be represented explicitly through values in tables. Knowledge of only one language is must to access all data like as attribute definitions and description of the table, integrity constraints, action to be taken when constraints are security information and violated.
Guaranteed Access Rule
Every piece of data in the relational database can be accessed through using a combination of a table name. The primary key value which identifies a column and the row name will identify the cell. The advantage of this is that user productivity is better since there is no requirement resort to using physical pointers addresses. Gives data independence.
Systematic Treatment of Null Values
RDBMS handles records which have unknown values in a predefined way. It distinguishes among blanks, zeroes and nulls in records and handles like values in a consistent manner which produces correct answers, calculations and comparisons.
Active On-Line Catalog Based on the Relational Model
The description of a database and its contents are database tables and thus can be queries on-line through the data language. The Data Base Administrator’s productivity is improved since modifications and additions to the catalog can be done with the similar commands which are used to access any other table. All queries and reports are done using this table.
Comprehensive Data Sub-language Rule
A RDBMS may support various languages, but atleast one of them permits the user to do all of the following: query, define table view and update data, set authorization, set integrity constraints and define transactions.
View Updating Rule
Any view is theoretically updateable if modifications can be made to the tables which effect the desired modifications in the view. The Data consistency is ensured because changes in the underlying tables are transmitted to the view they support. Logical data independence decrease maintenance cost.
High Level Inserts, Update and Delete
RDBMS supports insertion, deletion and updation at a table level. By this the RDBMS can improve performance through optimizing the path to be undertaken to perform the action. Ease of use is improved because commands act on set of records.
Physical Data Independence
The execution of the application programs and requests is not affected through the changes in the storage methods and physical data access. DBA’s (Database administrators) can make the modification to physical access and storage methods that improve performance but do not modify in the application programs or requests. This decrease the maintenance costs.
Logical Data Independence
Logical modifications in tables and views like as adding or deleting columns or changing field lengths do not necessitate modifications in application programs or in the format of adhoc requests.
Integrity Independence
Like table or view definitions, the integrity constraints are stored in the on-line catalog and thus can be changed without necessitating changes in application programs or in the format of the requests.
Distribution Independence
Application programs are not affected through modification in the distribution of the physical data.
Non-subversion Rule
Different levels of the language cannot bypass or subvert the integrity rules and constraints. By this rule, in order to adhere, RDBMS must have an active on-line catalog which contains the constraints.