Electronic Medical Record System
Electronic Medical Record System

Wednesday, January 18, 2006


A relational database management system (RDBMS) is a database management system (DBMS) that is based on the relational model as introduced by Edgar F. Codd.

Edgar F. "Ted" Codd (August 23, 1923April 18, 2003) was a British computer scientist who made seminal contributions to the theory of relational databases. While working for IBM, he created the relational model for database management. He made other valuable contributions to Informatics, but the relational model, a very influential general theory of data management, remains his most memorable achievement.

Edgar Frank Codd was born at Portland, Dorset, in England. He studied mathematics and chemistry at Exeter College, Oxford, before serving as a pilot in the Royal Air Force during the Second World War. In 1948 he moved to New York to work for IBM as a mathematical programmer. In 1953, angered by Senator Joseph McCarthy, Codd moved to Ottawa, Canada. A decade later he returned to the USA and received his doctorate in computer science from the University of Michigan in Ann Arbor. Two years later he moved to San Jose, California to work at IBM's Almaden Research Center.
In the 1960s and 1970s he worked out his theories of data arrangement, issuing his paper "A Relational Model of Data for Large Shared Data Banks" in 1970, after an internal IBM paper one year earlier. To his disappointment, IBM proved slow to exploit his suggestions until commercial rivals started implementing them.
Initially, IBM refused to implement the relational model in order to preserve revenue from IMS/DB. Codd then showed IBM customers the potential of the implementation of its model, and they in turn pressured IBM. Then IBM included in its Future System project a System R subproject — but put in charge of it developers who where not thoroughly familiar with Codd ideas, and isolated the team from Codd. As a result, they did not use Codd's own Alpha language but created a non-relational one, SEQUEL. Even so, SEQUEL was so superior to pre-relational systems that it was copied, based on pre-launch papers presented at conferences, by Larry Ellison in his Oracle DBMS, which actually reached market before SQL/DS — due to the then-already proprietary status of the original moniker, SEQUEL had been renamed SQL.
Codd continued to develop and extend his relational model, sometimes in collaboration with Chris Date. One of the normalized forms in Database normalization — the Boyce-Codd Normal Form, is named after Codd. As the relational model started to become fashionable in the early 1980s, Codd fought a sometimes bitter campaign to prevent the term being misused by database vendors who had merely added a relational veneer to older technology. As part of this campaign, he published his 12 rules to define what constituted a relational database. His campaign extended to the SQL language, which he regarded as an incorrect implementation of the theory. This made his position in IBM increasingly difficult, so he left to form his own consulting company with Chris Date and others.
Edgar Codd also coined the term OLAP and wrote the twelve laws of online analytical processing. Codd also contributed knowledge in the area of cellular automata.
Codd received a Turing Award in 1981.
Edgar F. Codd died of heart failure at his home in Williams Island, Florida at the age of 79 on Friday April 18th, 2003.

History of the term
Codd introduced the term in his seminal paper "A Relational Model of Data for Large Shared Data Banks". In this paper and later papers he defined what he meant by relational. One well-known definition of what constitutes a relational database system is Codd's 12 rules. However, many of the early implementations of the relational model did not conform to all of Codd's rules, so the term gradually came to describe a broader class of database systems. At a minimum, these systems:
presented the data to the user as relations (a presentation in tabular form, i.e. as a collection of tables with each table consisting of a set of rows and columns, can satisfy this property)
provided relational operators to manipulate the data in tabular form
The first systems that were relatively faithful implementations of the relational model were from the IBM UK Scientific Centre at Peterlee; IS1 (1970-1972) and its followon PRTV (1973-1979). The first system sold as an RDBMS was Multics Relational Data Store, first sold in 1978. Others have been Berkeley Ingres QUEL and IBM BS12.

Current usage
There is some disagreement about what a "relational" DBMS is.
The most popular definition of a RDBMS is relatively imprecise; some argue that merely presenting a view of data as a collection of rows and columns is sufficient to qualify as a RDBMS. Typically, products that qualify as a RDBMS under this interpretation implement some of Codd's 12 rules, but most popular database systems do not support them all.
A second school of thought argues that if a database does not implement all of Codd's rules, it is not relational. This view, shared by many theorists and other strict adherents to Codd's principles, would disqualify many database systems as not "truly relational". In fact, any database that uses the SQL (Structured Query Language) to access and modify data is not an RDBMS under this definition. Advocates of this philosophy refer to systems that follow some but not all of the rules as Pseudo-Relational Database Management Systems (PRDBMS). For clarification, they often refer to RDBMSs that do follow all of the rules as Truly-Relational Database Management Systems (TRDBMS).
Today, almost all RDBMSs employ SQL as their query language but alternatives have been proposed and implemented. Alphora's Dataphor is a commercially available RDBMS that follows all of Codd's rules - both groups recognising it as a RDBMS.

Dynamic variations
Another common complaint about existing RDBMS is that they are too "static". Speculation is starting to build about the next generation of "dynamic relational" database systems in which columns can be dynamically "created", dynamically sized, and dynamically typed (or type-free, also known as "context typing" in some circles). Each row could be implemented as a map (dictionary or associative array) and missing columns for any given row are simply represented as blank or empty. Some say this violates the true relational model, but others counter that a map is an only an implementation detail. In this viewpoint, a "missing column" is simply a matter of interpretation and presentation choice. Such a system could be used where rapid prototyping or competitive agility is necessary for the particular domain (industry). It may also simplify database usage with dynamic programming languages such as Perl, Ruby, PHP, etc. Extensions may allow formal schemas to be added gradually such that some columns can be designated "required" and/or given specific types or formatting rules