This is the parent of the database to implement 12 implementation recommendations for realizing relational database management systems.
CODD's 12 Rules
Dr. E.F. CODD, An IBM Research, First Developed The Relational Data
Model in 1970. in 1985, Dr. Codd Published A List of 12 Rules That Concisely
Define An IDEAL RELATIONAL DATABASE, WHICH HAVE PROVIDED A Guideline for the
Design Of All Relational Database Systems Ever Since.
I use the Term "Guideline" Because, To Date, No Commercial Relational Database
System full conforms to all 12 rules. They do represent the relatithional ideal,
Though. for a few Years, Scorecards WERE Kept That Rated Each Commercial
Product's Conformity To Codd's Rules. Today, The Rules Are Not Talked About
AS MUCH BUT Remain A Goal for Relational Database Design.
FOLLOWING IS A List of Codd's 12 Rules, Including His Original Name for Each Rule
And A Simplified Description. I Also Have Included a Note Where Certain Rules Are
Problematic TO IMPLEMENT. DON 'T WORRY IF Some of these Items Are Confusing To
YOU, AS WE MOVE FURTHER THROUGH this newsletter Series we will fill in the details.
Rule 1: The Information Rule
All Data Should Be Presened to The User In Table Form. Last Week's Newsletter
Already Discussed The Basics of this rule.
Rule 2: Guaranteed Access Rule
All Data Should Be Accessible WITHOUT Ambiguity. This Can Be Acccomplished
THROUGH a Combination of the Table Name, Primary Key, And Column Name.
Rule 3: Systematic Treatment of Null Values
A field shouth be unloaded to remain empty. This Involves the support of a null
Value, Which is distinct from an Empty string or a number with a value of zero.
Of Course, this Can't Apply to Primary Keys. In Addition, MOST DATABASE
Implementations support The Concept of a NUN- NULL FIELD CONSTRAINT THATSNULL VALUES IN A Specific Table Column.
Rule 4: Dynamic On-Line Catalog Based on The Relational Model A Relational
Database Must Provide
Access to Its Structure Through The Same Tools That Area Used to Access The Data.
This is usually acid.
Rule 5: CompRehensive Data Sublanguage Rule
The Database Must Support at Least One Clearly Defined Language That Includes
Functionality for Data Definition, Data Manipulation, Data Integrity, And Database
Transaction Control. All Commercial Relational Databases Use Forms of the Standard
SQL (Structured Query Language) as Their Supported Comprehensive Language.
Rule 6: View Updating Rule
Data can Be Presented to the user in diffins, caled views.
Each View Should Support The Same Full Range of Data Manipulation That Direct-Access To a Table Has Available. In Practice, Providing Update and Delete Access To
Logical views is difficult and is not fully supported by Any Current Database.
Rule 7: High-Level INSERT, UPDATE, AND DELETE
Data Can Be Retrieved from a relational database in sets constructed of data from
Multiple Rows and / or Multiple Tables. this rule stats That Insert, Update, And Delete
Operations Should Be Supported for Any Retrievable Set Rather Than Just for a Single
Row in a single table.
Rule 8: Physical Data Independence
The user is isolated from the physical method of storing and retrieving information
From the database. Changes Can Be Made to the underlying architecture (hardware,
Disk Storage Methods WITHOUT Affecting How The User Accesses IT.
Rule 9: Logical Data Independencehow a User Views Data Should Not Change When The Logical Structure (Tables
Structure) of the database change. This rule is particularly difficult to satisfy.
Most Databases Rely On Strong Ties Between The User View of The Data and The User View of the Data and T
Actual structure of the underlying tables.
Rule 10: Integrity Independence
The Database Language (Like SQL) SHOULD Support Constraints on User INPUT THAT
Maintain Database Integrity. This rule is not fully us .. Most Major Vendors.
At a minimum, All Databases Do Preserve Two Constraints Through SQL. No Component
(See Rule 3) of a primary key.
IF a Foreign Key IS Defined in One Table, Any Value In It Must EXIST AS A Primary Key in another table.
Rule 11: Distribution Independence
A User Should Be Totally UnaWare of WHether OR NOT The Database IS Distributed (WHETER
Parts of the database exist in multiple location). A Variety of Reasons Make this rule
Difficult to Implement; I Will Spend Time Addressing these Reasons WHEN We discuss
Distributed Databases.
Rule 12: Nonsubversion Rule
There SHOULD Be No Way To Modify The Database Structure Other Than Through The
Multiple Row Database Language (Like SQL). Most Databases Today Support Administrative
Tools That Allow Some Direct Manipulation of The Datastructure. Over The Life of this Newsletter,
I Will Be Expanding on The Concepts Covered by Each of Codd's Rules. I Will Use The Relational
Query Language of Choice, SQL, To Illustrate Thase Concepts and Explain Relational Database
Structure in detail.
============================================================================================================================================================================================================= == An attached:
Title Relational Database Father Fenng (Reposted)
Keyword Edgar F. CODD Database Biography
Somewhere
http://www.racle.com/global/cn/oramag/oracle/03-jul/index.html?content.html
Edgar (TED) CODD, 1923-2003
Commemorative relationship database of the father
Everyone said that Edgar F. CODD (usually known as TED) is a talented person. One of his achievements is to develop a relational data management model in the 1970s - a complex and complete theory of storage and operation of a large number of business data. According to the relational database of CODD, the database has become the foundation of today's enterprises; bank relies on relational databases to track funds; retailers use them to monitor inventory level; human resources department uses them to manage employee accounts; libraries, hospitals and government agencies There are millions of records in which millions of records are stored; in fact, almost all companies in the world are using a certain capacity relationship database. Since CODD announced its theory, the relational database has become an industry with nearly $ 13 billion in industries.
early life
Ted Codd was born in 1923 in a big family in Portland, England, England. He once studied in Oxford University, majoring in mathematics and chemistry, serving in the Royal Air Force during the Second World War. After the Second World War, CODD went to New York and became a mathematics programmer of IBM. The first project made by CODD is to help build an early computer called an optional sequence electronic calculator (SSEC), which is said to have two layers of a city office building. In the mid-1960s, CODD received a Ph.D. in Computer Science in Michigan University. After that, he transferred to IBM's development laboratory located in San Jose, California, where he began to develop relational data management models (this is a large extent to a model of mathematics). It is too big to improve the early computers in the database, too right, so that it is not widely used in the enterprise. In the 1960s, the computer began to become economically effective and gradually be adopted by the private sector, and many standards and languages were developed specifically for enterprise applications. Two of these are two models for processing data: hierarchical models and relational network models. In the hierarchy model, the data record is associated with each other in a hierarchy; mainly records at the upper layer, subsequent record types in the lower branch. In the network model, the record set in the layer may belong to two different contained hierarchies in the adjacent upper layer. For these two models, writing query statements to retrieve information requirements to understand the navigation structure of the data itself, so this is a complex task, generally done by specialized programmers.
CODD proposes a new solution. In a series of reports in the 1970 innovative technical papers - "a relational model of data for larding data banks" (Relationship data model of large shared database), CODD recommends that data is independent of hardware. Store, programmers use a non-process language to access data. The key to the CODD solution is to save the data in a simple table consisting of rows and columns (in this table, the columns of similar data interacts each table) instead of saving data in a hierarchy. . According to the idea of CODD, database users or applications do not need to know the data structure to query the data. Soon after the paper issued the paper, CODD released a more detailed guiding principle and put forward 12 principles of its guidance to create relational databases. After the theoretical disclosure of CODD, it was not adopted immediately by IBM. IBM has made a lot of investment in a hierarchy database called IMS, so it allows other companies and entrepreneurs to consider how to further develop the theory of CODD. The leader of the leader is Larry O Ellison. He has developed the world's first commercial relational database management system in 1977. In the process, a company has founded a company, and later became oracle. the company. The rest is to say is the history of the database. But for TED CODD, history does not stay there. Although until the early 1980s, CODD has been working in IBM, but he also creating a consulting service company with long-term collaborators Chris Date, and until he died this year, CODD has also continued to study And publish an article about the standardization, analysis and data modeling of data. Learn more about Edgar (TED) CODD
Www.wikipedia.org/wiki/edgar_f._codd
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