Relational databases store data in tables with relationships between them, based on principles of relational algebra. Keys differentiate data and tables can be linked in various ways. Data is organized through normalization and manipulated using SQL. RDBMS is the most commonly used database format, with Oracle, IBM, and Microsoft being the leading companies.
A relational database consists of a collection of tables that store particular sets of data. The invention of this database system standardized the way data is stored and processed. The concept of a relational database derives from the principles of relational algebra, collectively implemented by the father of relational databases, EF Codd. Most of the database systems in use today are based on the relational system; however, relational databases are built into software purchased by individuals and businesses, so the database is usually invisible to the general public.
The history of the relational database began with Codd’s 1970 article, A Relational Model of Data for Large Shared Data Banks. This theory stated that data should be independent of any hardware or storage system and provided for automatic navigation between data elements. In practice, this meant that the data had to be stored in tables and that there were relationships between the different datasets or tables.
Database content
The relationship, which is a two-dimensional table, is the primary storage unit in a relational database. A relational database can contain one or more of these tables, with each table consisting of a unique set of rows and columns. A single record is stored in a table as a row, also known as a tuple, while data attributes are defined in columns or fields in the table. The data characteristics, or column, relate one record to another. Each column has a unique name and the content within it must be of the same type.
Cross-referenced tables
Tables can be linked together in various ways. Functional dependencies are formed when an attribute of one table refers to attributes of other tables. The simplest relationship is the one-to-one relationship, where one record in one table is related to another record in a separate table. A one-to-many relationship is a relationship in which one record in one table is related to multiple records in another table. A many-to-one relationship defines the reverse situation; more than one record in a single table refers to only one record in another table. Finally, in a many-to-many relationship, more than one record in one table refers to more than one record in another table.
Differentiating data
When referring to a relational database, a key is an entity in a table that distinguishes one row of data from another. The key can be a single column or it can be a group of columns that uniquely identifies a record. Tables can contain primary keys and foreign keys. Primary keys are used to differentiate records from one another; they can be a single attribute or a combination of attributes. Foreign keys relate tables in the database to each other and generally define parent-child relationships between tables. Also, a foreign key in one table can be a primary key in another.
Data organization
Data stored in tables is logically organized according to a particular purpose to minimize duplication, reduce data anomalies, and strengthen data integrity. The process by which data is logically organized is called normalization; not only simplifies the definition of data, but also regulates its structure. There are five modules in the standardization process, with each module meeting a more challenging condition. First normal form, 1NF, meets the minimum requirements for normality and has the least data integrity, while fifth normal form, or 5NF, structures data with the fewest anomalies and the best integrity.
The stored data is manipulated using a programming language called Structured Query Language or SQL. There are many varieties of SQL, but most are based on set theory relational operators such as and, or, not, and in, all of which are used to perform operations on data. Operations that can be used in relational databases include insert, select, update, and delete privileges.
Product options
As of the early 2010s, relational database management system (RDBMS), is the most commonly used database format; it is often used by businesses and corporations to help update and administer relational databases. Historically, there have been three leading RDBMS companies: Oracle®, which created the first commercial relational database in 1979; IBM®, which followed suit in 1982 with SQL Data System, later renamed DB2®; and Microsoft®, which bundled with SQL Server® 4.2 in 1992. Other companies also offer RDBMS products, most of which can be purchased from the company’s Web site or at retail stores that sell computer software, and prices vary by company.
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