Edgar Frank Codd

Edgar Frank Codd (August 23rd 1923 - April 18th 2003) was a British data processing specialist . He is regarded as the inventor of the relational Modèle of SGBDR. In spite of the success of the language SQL which followed, Edgar F. Codd will denounce this tool which he regards as an incorrect interpretation of his theories.

The article of E.F. Codd which founds the relational model is “has Relational Model off Dated for Broad Shared Data Banks" , CACM 13, No 6, June 1970 , but the first description of this model had already been published the previous year in a report: “Derivability, Redundancy, and Consistency off Stored Relations in Broad Dated Banks”, IBM Research Report RJ599 .

Biography

Edgar Frank Codd was born in Portland in the Dorset. He studied mathematics and chemistry at the University of Exeter, Oxford, before being useful as a pilot in Royal Air Force during the Second world war. In 1948 he moved in New York to work at IBM as mathematical programmer. In 1953, irritated by the senator Joseph McCarthy, Codd emigrated in Ottawa. It is only one decade later that it returned to the United States and accepted its doctorate in data processing of the University of Michigan with Ann Arbor. Two years after it joined the research center of Almaden from IBM with San Jose in California.

In years 60-70 it establishes its theories of arrangement of data which it published in 1970 in its article “a related model of the data for large divided Data banks. ” With its disappointment, IBM was long in exploiting its suggestions and the first applications of its theories were developed by concurrent companies. It was for example the case for the Oracle database developed by Larry Ellison according to the ideas of Codd.

Codd continued to develop and extend its relational data model, sometimes in collaboration with Chris Date. One of the normal forms in the basic standardization of data, the normal form of Boyce-Codd, is baptized name of Codd.

Edgar Codd also invented limit OLAP and wrote the twelve laws of the analytical treatment on line. Codd also contributed to knowledge in the sector of the cellular automats.

Codd received the Price Turing in 1981.

On Friday, April 18, 2003, Edgar F. Codd died of an cardiac arrest in its residence on the island of Williams (Florida) at the 79 years age.

12 rules of Codd

The 12 rules of Codd are a whole of rules enacted by Edgar F. Codd, conceived to define what is required of a basic management system of data (DBMS) so that it can be regarded as relational (SGBDR).

Rule 1: The rule of information:

All information in the database is represented of one and only one manner, namely by values in fields of columns of tables.

Rule 2: The guaranteed rule of access:

All the data must be accessible without ambiguity. This rule is primarily an adjustment of the fundamental condition for primary keys. It indicates that each individual scalar value in the database must be logically accessible by indicating the name from the table containing, the name of the column containing and the principal value primary of the line containing.

Rule 3: Systematic treatment of the zero values:

the management system of databases must make it possible each field to remain null (or vacuum). Specifically, it must support a representation " of missing information and information inapplicable" who is systematic, distinct from all the regular values (for example, " distinct from zero or all other numbers, " in the case of numerical values), and this independently of the type of data. That also implies that such representations must be managed by the management system of databases in a systematic way.

Rule 4: Catalog in line credit based on the relational model:

the system must support a catalog in line, integrated, relational, accessible to the users authorized by means of their regular language of interrogation. The users must thus be able to reach the structure of the database (catalogs) employing the same language of interrogation that they employ to reach the data of the database.

Rule 5: The rule supplements under-language of data:

the system must support at least a relational language which:

(A) has a linear syntax

(b) can be employed interactivement and in application programs,

(c) supports operation of definition of extra informations (including definitions of sights), of handling of data (updated as well as recovery), constraints of safety and integrity, and operations of management of transaction (to begin, validate and cancel a transaction).

Rule 6: The rule of update of the sights:

All the sights theoretically being able to be updated must be able the being by the system.

Rule 7: Insertion, update, and high level obliteration:

the system must support the operation by batch of insertion, update and suppression. This means that data can be extracted from a relational database in units consisted data resulting from several tuples and/or the multiple ones counts. This rule explains why insertion, the update, and the operations of obliteration should be supported as well for batches of tuples resulting from several tables as just for a single tuple resulting from a single table.

Rule 8: The physical independence of data:

modifications at the physical level (how the data are stored, so in the dependant lines or lists etc…) do not require a change of an application based on the structures.

Rule 9: The logical independence of data:

the changes at the logical level (tables, columns, lines, etc) should not require a change in the application based on the structures. The independence of logical data is more difficult has to reach than the physical independence of data.

Rule 10: The independence of integrity:

Of the constraints of integrity must be indicated separately application programs and be stored in the catalog. It must be possible progressively to change such constraints without affecting the existing applications unnecessarily.

Rule 11: The independence of distribution:

the distribution of the parts of the database to various localizations should be invisible to the users of the database. The existing applications should continue to function successfully:

(A) when a distributed version of the management system of databases is initially presented; and

(b) as of the existing data is redistributed in the system.

Rule 12: The rule of nonsubversion:

If the system provides an interface of low level, then this interface cannot be employed to circumvent the system, for example, to circumvent a relational constraint of safety or integrity.

One considers sometimes a rule 0, which stipulates that the entirety of the functions of the SGBDR must be accessible by the relational model. Codd formulated six other rules in 1990.

See too

Normal Boyce-Codd Form, or normal form BCNF

OLAP

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