B5: Relational Database Theory

A relational database is a database whose symbols are organized into a collection of relations. Relational Database was born in 1970 when a researcher at IBM wrote a paper about the process. Relation appeals to the notion of relationships between things. Before the invention of relational database, databases were flat. Information were stored in one long text file called tab delimited file. Each entry in the tab delimited file is separated with a vertical bar (|). Here's an example of a tab delimited file:

Lname, FName, Age, Salary|Smith, John, 35, $280|Doe, Jane, 28, $325|Brown, Scott, 41, $265|Howard, Shemp, 48, $359|Taylor, Tom, 22, $250

It is difficult to search for a specific information because everything is grouped together. A relational database makes it easier to compare information because of the arrangement of related data in columns. A typical relational database has anywhere from 10 to more than 1,000 tables. Each table contains a column or columns that other tables can key on to gather information from that table.

Many people use the word table an an alternative to relation. However, the term relation does not equal the term table. Thus, they are not synonymous. For example, every relation can be shown as a table, but not every table is a representation of some kind of relation. The figure below shows a table but no apparent relation is depicted.

A database management system (DBMS) is a piece of software for managing databases and providing access to them. A DBMS responds to commands given by application programs executing on behalf of users. Commands are written in the database language of DBMS (or SQL). Response include completion codes, messages and results of queries.

Dmitriy Voznyak talked about relational database. He said that relational database is the most popular in the market. He also named some common relational database management systems including Oracle, Sybase, Microsoft SQL Server, Access, and Ingres. The only thing that I want to comment on is his definition of relational database. He did not emphasize that although relational databases are tables, they are not mutually exclusive.

Taylor Castonguay talked about the five normal forms. These forms are designed to prevent update anomalies and data inconsistencies. However, I still don't fully understand what the differences are between these forms.

J Schwakoff gave good instances when we encounter databases. He emphasized that they are used in online banking, ordering something online, checking grades, and even signing up for our courses online.

Reference:
Darwen, Hugh. An Introduction to Relational Database Theory. 2010.