Codd, after his extensive research on the Relational Model of database systems, came up with twelve rules of his own, which according to him, relational database definition pdf database must obey in order to be regarded as a true relational database. These rules can be applied on any database system that manages stored data using only its relational capabilities.
This is a foundation rule, which acts as a base for all the other rules. Rule 1: Information Rule The data stored in a database, may it be user data or metadata, must be a value of some table cell. Everything in a database must be stored in a table format. No other means, such as pointers, can be used to access data.
Rule 3: Systematic Treatment of NULL Values The NULL values in a database must be given a systematic and uniform treatment. Rule 4: Active Online Catalog The structure description of the entire database must be stored in an online catalog, known as data dictionary, which can be accessed by authorized users. Users can use the same query language to access the catalog which they use to access the database itself. Rule 5: Comprehensive Data Sub-Language Rule A database can only be accessed using a language having linear syntax that supports data definition, data manipulation, and transaction management operations. This language can be used directly or by means of some application.
If the database allows access to data without any help of this language, then it is considered as a violation. Rule 6: View Updating Rule All the views of a database, which can theoretically be updated, must also be updatable by the system. Rule 7: High-Level Insert, Update, and Delete Rule A database must support high-level insertion, updation, and deletion. This must not be limited to a single row, that is, it must also support union, intersection and minus operations to yield sets of data records. Rule 8: Physical Data Independence The data stored in a database must be independent of the applications that access the database. Any change in the physical structure of a database must not have any impact on how the data is being accessed by external applications. Any change in logical data must not affect the applications using it.
For example, if two tables are merged or one is split into two different tables, there should be no impact or change on the user application. This is one of the most difficult rule to apply. Rule 10: Integrity Independence A database must be independent of the application that uses it. All its integrity constraints can be independently modified without the need of any change in the application.
This rule makes a database independent of the front-end application and its interface. Rule 11: Distribution Independence The end-user must not be able to see that the data is distributed over various locations. Users should always get the impression that the data is located at one site only. This rule has been regarded as the foundation of distributed database systems.
Rule 12: Non-Subversion Rule If a system has an interface that provides access to low-level records, then the interface must not be able to subvert the system and bypass security and integrity constraints. Please forward this error screen to 67. The general structure of a relational database. RDBMSs have been a common choice for the storage of information in databases used for financial records, manufacturing and logistical information, personnel data, and other applications since the 1980s. In 1974, IBM began developing System R, a research project to develop a prototype RDBMS. The term “relational database” was invented by E.
Codd introduced the term in his research paper “A Relational Model of Data for Large Shared Data Banks”. In this paper and later papers, he defined what he meant by “relational”. Provide relational operators to manipulate the data in tabular form. 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 theory. By this definition, RDBMS products typically implement some but not all of Codd’s 12 rules. As of 2009, most commercial relational DBMSs employ SQL as their query language. Alternative query languages have been proposed and implemented, notably the pre-1996 implementation of Ingres QUEL.
NoSQL databases eat into the relational database market”. Funding a Revolution: Government Support for Computing Research. Fundamentals of Relational Database Management Systems. New Database Software Program Moves Macintosh Into The Big Leagues”. This page was last edited on 14 March 2018, at 15:59. This article needs additional citations for verification. A relational database is a digital database based on the relational model of data, as proposed by E.