[Database Modeling] Relational Model (2)
3. 12 Rules of Relational Database suggested by E.F.CODD (1)
- Rule 0 (Basic Rule)
A system must be qualified for a "relational model" not only as "database", but also management system". To be qualified for an RDBMS (Relational Database Management System), the system must use its relational method for managing database.
- Rule 1 (Informational Rule)
All of the information of a database must be expressed in one way only. In other words, it must be expressed as a value in one column in one row.
- Rule 2 (Guaranteed accessing rule)
Every data must be accessed without ambiguity. This rule means a "Primary Key" is needed. The values of individual scalars of a database must be logically addressable, if table names, column
names, and row's primary keys including them are assigned.
- Rule 3 (Systematic management of NULL value)
A DBMS must allow each filed have a null value. (In other words, each field can be empty.) Especially, a DBMS must support "no information" or "inactive information". However,
it must be systematic and distinguished from other values. (For instance, a number must be "0" or distinguished from other numbers.) The expression about "no information" or "inactive information" means the data type must be independent. This rule implies that those expressions must be systematically handled in a DBMS.
- Rule 4 (Relational-model-based active online database catalog)
A system must support online and in-line relational catalogs. This relational catalog must be
accessed by allowed users with usual query languages. In other words, users must be able to access to the database structure (catalog) with the same language as the one for accessing to the data.
- Rule 5 (Comprehensive rule for data auxiliary language)
A system must support at least one relational language, and the language must have the following features.
1) It must have linear grammars.
2) It can be interactively used and also used in an application program.
3) It must support data definition operations. (It also must define views.) It must support data manipulation operations. It must support security, integrity, constraint conditions, and transaction management (begin, commit, rollback).
- Rule 6 (View renewal rule)
Theoretically, renewable views must be able to be updated by a system.
Last modified on Monday, 10 Aug 2015, 15:50