Properties of RDBMS

Definition of Relational

A DBMS can be considered as relational if it follows the 3 rules stated below

a. All information must be held in tables.
b. Retrieval of data must be possible by using select, join & project.
c. All relationships between data must be explicitly represented in that data itself.

Codd's Rules

To define the requirements for an RDBMS more rigorously, Court has stated 12 rules commonly called as Codd's Rules. A product is said to be truly relational if it follows all the rules, but no product exists which follows them all. The Rule 0 covers all other rules stating that 'Any truly relational database must be manageable entirely through its own relational capabilities'.

Rule

The Information Rule: 'All the information in an RDBMS is explicitly I represented in one way, by values in a table'. Anything that does not exist in a table does not exist at all. All the information including table names, view names, column names and column data types must be stored in tables within database. Tables that. hold such information constitute the Data Dictionary.

Rule 2

The Rule of Guaranteed Access: 'Every item of data must be logically addressable by resorting to a combination of table name, primary key and column name'. It means that given a table name, you will necessarily find one and only one value. In case of Oracle RDBMS, the definition of primary key is mandatory.

Rule 3

Systematic Treatment of Null values: 'Inapplicable or missing information can be represented through null values'. An RDBMS should support the representation of null in place of column values to represent unknown values or inapplicable values

Rule 4

The Database description Rule: The description of the database is held in the same ways as ordinary data that is in tables and columns and is accessible to authorized users'. Table, view and authorization access definitions should be held in exactly same manner, i.e. as tables and views. These tables should be accessible like other tables through SQL statements.

Rule 5

The Comprehensive sub language rule: 'There must be at least one language which is comprehensive in supporting data definition, view definition, data manipulation, integrity constraints, authorization and transaction control'. This means that there must be atleast one language with a well defined syntax which can be used to manage the database completely.

Rule 6

The View Updating Rule: 'All the views that are theoretically updatable are updatable by the system'. Most RDBMS allow update of simple theoretically updatable views, but disallow attempts to update complex views.

Rule 7

The Insert and Update Rule: 'The capability of handling a base or a derived table as a single operand applies not only to the retrieval of data but also to the insertion, update and deletion of data'. This means that all Select, Update, Delete and insert must be available and operate on sets of row in any relation, as against row at a time processing.

Rule 8

The Physical Independence Rule: 'User access to the database, via terrminal monitors or application programs, must remain logically consistent whenever changes to the storage representations, or access methods to the data are changed'. The behavior of application programs and user terminal activity should be predictable and based on the logical definition of the database and this behavior should remain unchanged irrespective of the changes in the physical definition, as long as the logical definition of the database is unchanged.

Rule 9

The Logical Independence Rule: 'Application programs and terminal activities must remain logically unimpaired whenever information preserving changes of any kind, that are theoretically permitted are made to the base tables". The logical data independence specifies that the application programs and terminal activity should be independent of the logical structure and hence changes in logical structure should not impair the application programs.

Rule 10

Integrity Independence Rule: 'All integrity constraints must be definable in the data (no suggestions) and storable in the catalogue, not in the application program'. The integrity rules are, 1. No component of a primary key can have missing values this is the basic rule of Entity Integrity. 2. For each distinct foreign key value there must exist a matching primary key value in the same domain. Conformation to this rule ensures Referential Integrity.

Rule 11

would mean that an arbitrary collection of relations, databases running on a Mix of machines and operating systems and connected by a variety of networks can function as if they were available on a single database.

Distribution Rule: 'The system must have a data sub language which can support distributed databases without impairing application programs or terminal activities'. A complete distributed database support

Rule 12

Non Subversion Rule: 'If the system has a low level languages, this language cannot be used to bypass the integrity rules and constraints expressed in higher level relational language'. Some products only build a relational front end to their non relational DBMS which make possible subversion of constraints. This shall not be allowed.

Domain Name Search