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| Re: Codd's Rule of RDBMS [message #104078 is a reply to message #102659] |
Thu, 22 July 2004 23:41  |
jayaprakash
Messages: 2
Registered: July 2004
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Junior Member |
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All data must be accessible with no ambiguity. This rule is essentially a restatement of the fundamental requirement for primary keys. It says that every individual scalar value in the database must be logically addressable by specifying the name of the containing table, the name of the containing column and the primary key value of the containing row.
3. Systematic treatment of null values:
The DBMS must allow each field to remain null (or empty). Specifically, it must support a representation of "missing information and inapplicable information" that is systematic, distinct from all regular values (for example, "distinct from zero or any other number," in the case of numeric values), and independent of data type. It is also implied that such representations must be manipulated by the DBMS in a systematic way
4. Active online catalog based on the relational model:
The system must support an online, inline, relational catalog that is accessible to authorized users by means of their regular query language. That is, users must be able to access the database's structure (catalog) using the same query language that they use to access the database's data.
5. The comprehensive data sublanguage rule:
The system must support at least one relational language that :(a) Has a linear syntax :(b) Can be used both interactively and within application programs, :(c) Supports data definition operations (including view definitions), data manipulation operations (update as well as retrieval), security and integrity constraints, and transaction management operations (begin, commit, and rollback).
6.The view updating rule:
All views that are theoretically updatable must be updatable by the system.
7. High-level insert, update, and delete:
The system must support set-at-a-time insert, update, and delete operators.
8. Physical data independence:
The physical representation of the data must be invisible to the user, so that the user can manage the data according to need rather than according to the way it is stored.
9. Logical data independence:
If a user's view of the data has been defined, then changing the logical structure of the data (tables, columns, rows, and so on) must not change the user's view.
10. Integrity independence:
Integrity constraints must be specified separately from application programs and stored in the catalog. It must be possible to change such constraints as and when appropriate without unnecessarily affecting existing applications.
11. Distribution independence:
The distribution of portions of the database to various locations should be invisible to users of the database. Existing applications should continue to operate successfully : :(a) when a distributed version of the DBMS is first introduced; and :(b) when existing distributed data are redistributed around the system.
12. The nonsubversion rule:
If the system provides a low-level (record-at-a-time) interface, then that interface cannot be used to subvert the system, for example, bypassing a relational security or integrity constraint. preview not available. Click the link for more information.
Further Queries:-
http://encyclopedia.thefreedictionary.com/Codd's%2012%20rules
Oracle Not supported Codd's Rule is
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The only one of Codd's rules that Oracle doesn't support is the systematic treatment of null values. The empty character string in general is treated as a NULL in Oracle.
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