There are 12 rules developed by EF-Codd for RDBMS in 1970. An RDBMS maintain least 6 rules follow.
- Information representation->
It is the first rules of Codd for RDBMS that identify to represent explicitly and logically information by entering into the exiting table. A table that contains a record, as well as schema, should be represented all information.Data store in data dictionary it also maintains as a tabular format.
2. Guaranteed access->
This rule refers to get all value which is stored in a table. The data table allows fetching infrastructure and related value of each row and column. The clank spaces can also we read and process.
3. Systematic treatment of null value->
If RDBMS the null value identified as missing and inapplicable only the database management system must have a structured method for representing a null value. In RDBMS we can easily access the null information and also support in SQL.
4. Database description rules->
The description database is stored and maintained in the form of row and column. This rule allows to the user for managing the information of the user for managing the information on the base of given permission similar to a programming language. The dictionary should be represented giving the RDBMS can be examined by the SQL.
5. Comprehensive data sublanguage->
The RDBMS must be manageable to the SQL which is the adjusting of RDBMS definition, view, integrity constraints transaction boundary etc
6. View updating->
The view can be defined using a combination of base table and properly of day table must be updating RDBMS.
7. High-level update insert and delete->
An RDBMS must be for possible insert, delete and update data on the table that also we support high-level objection relation etc
8. Physical data independence->
The RDBMS change mode to physical store the representing access method do not require changing at the application level.
9. Logical data independence->
Application program should not be affected by the mode to the base table. It means the table contains are not effecting after changing at the application level.
10. Distribution rule->
The components of RDBMS must have distribution independent. It means the RDBMS package can be saved at multiple user ar machines for data processing on RDBMS support client and server design for data sharing and support multi-platforms.
If are RDBMS support facility to control b application programme for operating the data table. An application programme using one-row processing at a time for database access using entity and referential method.
12. Integrity rule->
The integrity support applies to the particular database must be defined in SQL or another relation sublanguage. This integrity subbertion must be managed in the database, not in the application programme.
Database management system allows to store the data into an organized format and create the key field for unique identification. It means the key field cannot store dedicated record ate the tome of processing we define the key field form the number of attributes of an entity.
- Primary key->It is key that uses in the database for uniquely identified of each record. It means some records ever stored in a primary key repeated attribute. A table that contains only one primary key so it can also be identified as minimal super key.
- Super key->It is a key that signed attribute. This key for an entity is a set of one and more attributes whose combine value uniquely identifies the entity set. The super key use of more than one attributes.
- Candidate key->It is an attribute or setup attribute that uses unique identification for data storage. The attribute or combination of key attributes known as candidate key in this a key is primary and another key is alternative key. There is only one primary key on a table but they can be multiple candidates key.
- Composite key->It is also key that use in the attribute for assign in more than one columns part of primary key. The composite key use for unique identification by a single field more than one field. A composite key is a group of the field. A composite key is a group of the field. A composite key is a group of the field that is combined together for unique identification.
- Secondary key->It is an attribute or combination of attributes that may not be a candidate key basically use to manage multiple tables with a secondary key.
- Foreign key->In a relation attributes who information correspond to the value of a key field in another relationship that is known as a foreign key. The foreign key may be primary key in another relation. It is used for reference with another table through the key field.