Relational database management system

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.

History of the term

E. F. 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 an RDBMS is imprecise and not strictly based on relational theory; some argue that merely presenting a view of data as a collection of rows and columns is sufficient to qualify as an RDBMS. Typically, products that qualify as an RDBMS under this interpretation implement some of Codd's 12 rules, but no popular database system supports them all. The vast majority of real-world database installations fall into this category.

A second, theory-based 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 RDBMSs as Truly-Relational Database Management Systems (TRDBMS).

Today, almost all DBMSs employ SQL as their query language, but alternatives have been proposed and implemented. Very few have become commercial products. Alphora's Dataphor is a commercially available RDBMS that follows all of Codd's rules — both groups recognizing it as a RDBMS.

Criticisms

Here are criticisms and complaints that can be found with regard to current RDBMS:

Vendors don't explore optional query languages outside of SQL. Many feel that SQL needs an update or overhaul, being about 30 years old.

They are usually statically-typed. Some feel that dynamically-typed or optional columns may make RDBMS more useful for prototyping or for domains where being nimble in a market is important. (Optional columns are implemented by returning null or blank for columns not defined in a given record.)

No scaling - Often one needs a small, lightweight RDBMS for internal (application-specific) processing or experimental applications. After the product becomes more formal, one then wants to upscale to more formal "big iron" RDBMS. However, existing products often do not provide a light-duty version that is compatible with the more formal version. Thus, one often ends up using a different vendor's product for the low-end, but they are not fully compatible with the eventual vendor. A good example of a working light-weight<->big iron product model is Microsoft SQL Server and SQL Server Express. Microsoft appear to have pushed up the SQL Express version to replace their previous desktop data technology, MS Access, which was almost the byword for low-scalability/portability. This point is being addressed.

Over-ubiquity - Not all data models require a relational data store, but most developers will pick one up and run with it anyway. As a result, most non-relational DBMS have been starved of development time and innovation.

External links

Database Debunkings - Critical point of view that argues that it is important that the predicate relational should be reserved for those database systems that are fully faithful to the relational model.

Are SQL Server, DB2, and Oracle really relational? - An article by Itoi Blomgren, Michiko. (2003)

A Brief History of IT Management and the RDBMS - A brief history of modern RDBMS technology from the operational perspective of information technology management practice.

Database management systems

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History of the term

Current usage

Criticisms

See also

External links