# RDBMS (Relational Database Management System)

The general structure of a relational database.

A relational database management system (RDBMS) is a database management system (DBMS) that is based on the relational model as invented by E. F. Codd, of IBM's San Jose Research Laboratory. In 2016, many of the databases in widespread use are based on the relational database model.

RDBMSs have been a common choice for the storage of information in new databases used for financial records, manufacturing and logistical information, personnel data, and other applications since the 1980s. Relational databases have often replaced legacy hierarchical databases and network databases because they are easier to understand and use. However, relational databases have received unsuccessful challenge attempts by object database management systems in the 1980s and 1990s (which were introduced trying to address the so-called object-relational impedance mismatch between relational databases and object-oriented application programs) and also by XML database management systems in the 1990s. Despite such attempts, RDBMSs keep most of the market share, which has also grown over the years.

## Market share

According to DB-Engines, in 2016, the most widely used systems are Oracle, MySQL (open source), Microsoft SQL Server, PostgreSQL (open source), IBM DB2, Microsoft Access, and SQLite (open source).[1]

According to research company Gartner, in 2011, the five leading commercial relational database vendors by revenue were Oracle (48.8%), IBM (20.2%), Microsoft (17.0%), SAP AG|SAP including Sybase (4.6%), and Teradata (3.7%).[2]

According to Gartner, in 2008, the percentage of database sites using any given technology were (a given site may deploy multiple technologies):

• Oracle Database – 70%
• Microsoft SQL Server – 68%
• MySQL (Oracle Corporation) – 50%
• IBM DB2 – 39%
• IBM Informix – 18%
• Sybase IQ|SAP Sybase IQ – 14%

## History

In 1974, IBM began developing IBM System R|System R, a research project to develop a prototype RDBMS. However, the first commercially available RDBMS was Oracle, released in 1979 by Relational Software, now Oracle Corporation. Other examples of an RDBMS include IBM DB2|DB2, Adaptive Server Enterprise, and IBM. In 1984, the first RDBMS for Macintosh began being developed, code-named Silver Surfer, it was later released in 1987 as 4th Dimension and known today as 4D.[3]

## Historical usage of the term

The term "relational database" was invented by Edgar F. Codd at IBM in 1970. Codd introduced the term in his seminal paper "A Relational Model of Data for Large Shared Data Banks".[4] 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 composed of 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, which at a minimum:

• Present the data to the user as relation (database) (a presentation in tabular form, i.e. as a collection of tables with each table consisting of a set of rows and columns);
• Provide relational operators to manipulate the data in tabular form.

The first systems that were relatively faithful implementations of the relational model were from the University of Michigan; MICRO Relational Database Management System (1969), the Massachusetts Institute of Technology;[5] (1971), and from IBM UK Scientific Centre at Peterlee; IBM IS1 (1970–72) and its followon PRTV (1973–79). The first system sold as an RDBMS was Multics Relational Data Store, first sold in 1978. Others have been Ingres (database) and IBM BS12.

The most common definition of an RDBMS is a product that presents a view of data as a collection of rows and columns, even if it is not based strictly upon Relational model|relational theory. By this definition, RDBMS products typically implement some but not all of Codd's 12 rules.

A second school of thought argues that if a database does not implement all of Codd's rules (or the current understanding on the relational model, as expressed by Christopher J Date, Hugh Darwen and others), it is not relational. This view, shared by many theorists and other strict adherents to Codd's principles, would disqualify most DBMSs as not relational. For clarification, they often refer to some RDBMSs as truly-relational database management systems (TRDBMS), naming others pseudo-relational database management systems (PRDBMS).

As of 2009, most commercial relational DBMSes employ SQL as their query language.

Alternative query languages have been proposed and implemented, notably the pre-1996 implementation of QUEL query languages.

## References

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1. "DB-Engines Ranking of Relational DBMS". Retrieved 2016-10-01.
2. "Oracle the clear leader in \$24 billion RDBMS market". 2012-04-12. Retrieved 2013-03-01.
3. "New Database Software Program Moves Macintosh Into The Big Leagues". tribunedigital-chicagotribune. Retrieved 2016-03-17.
4. "A Relational Model of Data for Large Shared Data Banks"
5. SIGFIDET '74 Proceedings of the 1974 ACM SIGFIDET (now SIGMOD) workshop on Data description, access and control