Advanced Database Management System - Tutorials and Notes: Codd's Twelve Rules - Rule 4 - Dynamic Online Catalog Based on the Relational Model

Wednesday, 18 February 2015

Codd's Twelve Rules - Rule 4 - Dynamic Online Catalog Based on the Relational Model


Codd's Twelve Rules - Rule 4 - Dynamic Online Catalog Based on the Relational Model



Rule 4
Dynamic Online Catalog Based on the Relational Model
Rule
The database description is represented at the logical level in the same way as ordinary data, so authorized users can apply the same relational language to its interrogation as they apply to regular data.
Description
This rule requires that a relational database be self-describing. In other words, the database must contain certain system tables whose columns describe the structure of the database itself, or alternatively, the database description is contained in user-accessible tables. In other words, this rule insists a data dictionary that stores meta data.
Example
  • INFORMATION_SCHEMA system views in SQL Server, 
  •  INFORMATION_SCHEMA  information database in MySQL, and
  • Oracle Data dictionary resides in SYSTEM tablespace and can be accessed using the prefixes USER, ALL, or DBA.
Some DBMS that fulfills this property
SQL Server, MySQL, and Oracle.

No comments:

Post a comment

Featured Content

Multiple choice questions in Natural Language Processing Home

MCQ in Natural Language Processing, Quiz questions with answers in NLP, Top interview questions in NLP with answers Multiple Choice Que...

All time most popular contents