A relational database management system must manage its stored data using only its relational capabilities.
1. Information Rule
All information in the database should be represented in one and only one way - as values in a table.
2. Guaranteed Access Rule
Each and every datum (atomic value) is guaranteed to be logically accessible by resorting to a combination of table name, primary key value and column name.
3. Systematic Treatment of Null Values
Null values (distinct from empty character string or a string of blank characters and distinct from zero or any other number) are supported in the fully relational DBMS for representing missing information in a systematic way, independent of data type.
Null and N/A should be handled differently.
4. Dynamic On-line Catalog Based on the Relational Model
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.
Every database should have a catalog and description of the fields indices and mappings.
5. Comprehensive Data Sublanguage Rule
A relational system may support several languages and various modes of terminal use. However, there must be at least one language whose statements are expressible, per some well-defined syntax, as character strings and whose ability to support all of the following is comprehensible:
data manipulation (interactive and by program)
transaction boundaries (begin, commit, and rollback).
This refers to a structured query language (SQL).
6. View Updating Rule
All views that are theoretically updateable are also updateable by the system.
This refers to virtual tables created dynamically by joining other tables using SQL. There is a problem here: if a view does not contain the linking field, subsequent updates of that view would violate the relational integrity of the system.
7. High-level Insert, Update, and Delete
The capability of handling a base relation or a derived relation as a single operand applies nor only to the retrieval of data but also to the insertion, update, and deletion of data.
This refers to the ability to insert multiple records simultaneously.
8. Physical Data Independence
Application programs and terminal activities remain logically unimpaired whenever any changes aMay 23, 2006>
User interaction is independent of the physical location and access of the database.
9. Logical Data Independence
Application programs and terminal activities remain logically unimpaired when information preserving changes of any kind that theoretically permit unimpairment are made to the base tables.
This means that programs using the data continue to function even when the data is changed
10. Integrity Independence
Integrity constraints specific to a particular relational database must be definable in the relational data sublanguage and storable in the catalog, not in the application programs.
It is desireable to habe the database itself enforce the data rules, rather than the interfacing programs.
11. Distribution Independence
The data manipulation sublanguage of a relational DBMS must enable application programs and terminal activities to remain logically unimpaired whether and whenever data are physically centralized or distributed.
The system should work regardless of the location, or the degreee of aggregation of the data.
12. Nonsubversion Rule
If a relational system has or supports a low-level (single-record-at-a-time) language, that low-level language cannot be used to subvert or bypass the integrity rules or constraints expressed in the higher-level (multiple-records-at-a-time) relational language.
There needs to be a water-tight enforcement of the data rules without any exceptions.
Codd, E. (1985). "Is Your DBMS Really Relational?" and "Does Your DBMS Run By the Rules?" ComputerWorld, October 14 and October 21.
Elmasri, R., & Navathe, S. (1994). Fundamentals of Database Systems. 2nd ed. Redwood City, CA: The Benjamin/Cummings Publishing Co. pp. 283 – 285.
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