A relational database is a collection of data items with pre-defined relationships between them. These items are organized as a set of tables with columns and rows. Tables are used to hold information about the objects to be represented in the database. Quick and simple free tool to help you draw your database relationship diagrams and flow quickly using simple DSL language.
Databases have been a staple of business computing from the very beginning of the digital era. In fact, the relational database was born in 1970 when E.F. Codd, a researcher at IBM, wrote a paper outlining the process. Since then, relational databases have grown in popularity to become the standard.
Originally, databases were flat. This means that the information was stored in one long text file, called a tab delimited file. Each entry in the tab delimited file is separated by a special character, such as a vertical bar (|). Each entry contains multiple pieces of information (fields) about a particular object or person grouped together as a record. The text file makes it difficult to search for specific information or to create reports that include only certain fields from each record. Here's an example of the file created by a flat database:
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Lname, FName, Age, Salary|Smith, John, 35, $280|Doe, Jane, 28, $325|Brown, Scott, 41, $265|Howard, Shemp, 48, $359|Taylor, Tom, 22, $250
You can see that you have to search sequentially through the entire file to gather related information, such as age or salary. A relational database allows you to easily find specific information. It also allows you to sort based on any field and generate reports that contain only certain fields from each record. Relational databases use tables to store information. The standard fields and records are represented as columns (fields) and rows (records) in a table.
With a relational database, you can quickly compare information because of the arrangement of data in columns. The relational database model takes advantage of this uniformity to build completely new tables out of required information from existing tables. In other words, it uses the relationship of similar data to increase the speed and versatility of the database.
The 'relational' part of the name comes into play because of mathmatical relations. 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.
By storing this information in another table, the database can create a single small table with the locations that can then be used for a variety of purposes by other tables in the database. A typical large database, like the one a big Web site, such as Amazon would have, will contain hundreds or thousands of tables like this all used together to quickly find the exact information needed at any given time.
Relational databases are created using a special computer language, structured query language (SQL), that is the standard for database interoperability. SQL is the foundation for all of the popular database applications available today, from Access to Oracle.
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A relational database is a collection of data items with pre-defined relationships between them. These items are organized as a set of tables with columns and rows. Tables are used to hold information about the objects to be represented in the database. Each column in a table holds a certain kind of data and a field stores the actual value of an attribute. The rows in the table represent a collection of related values of one object or entity. Each row in a table could be marked with a unique identifier called a primary key, and rows among multiple tables can be made related using foreign keys. This data can be accessed in many different ways without reorganizing the database tables themselves.
SQL or Structured Query Language is the primary interface used to communicate with Relational Databases. SQL became a standard of the American National Standards Institute (ANSI) in 1986. The standard ANSI SQL is supported by all popular relational database engines, and some of these engines also have extension to ANSI SQL to support functionality which is specific to that engine. SQL is used to add, update or delete rows of data, retrieving subsets of data for transaction processing and analytics applications, and to manage all aspects of the database.
Data integrity is the overall completeness, accuracy and consistency of data. Relational databases use a set of constraints to enforce data integrity in the database. These include primary Keys, Foreign Keys, ‘Not NULL' constraint, ‘Unique' constraint, ‘Default' constraint and ‘Check' constraints. These integrity constraints help enforce business rules on data in the tables to ensure the accuracy and reliability of the data. In addition to these, most relation databases also allow custom code to be embedded in triggers that execute based on an action on the database.
Relationship Database Management System
A database transaction is one or more SQL statements that are executed as a sequence of operations that form a single logical unit of work. Transactions provide an 'all-or-nothing' proposition, meaning that the entire transaction must complete as a single unit and be written to the database or none of the individual components of the transaction should go through. In the relation database terminology, a transaction results in a COMMIT or a ROLLBACK. Each transaction is treated in a coherent and reliable way independent of other transactions.
Relationship Database Design
All database transactions must be ACID compliant or be Atomic, Consistent, Isolated and Durable to ensure data integrity.
Atomicity requires that either transaction as a whole be successfully executed or if a part of the transaction fails, then the entire transaction be invalidated. Consistency mandates the data written to the database as part of the transaction must adhere to all defined rules, and restrictions including constraints, cascades, and triggers. Isolation is critical to achieving concurrency control and makes sure each transaction is independent unto itself. Durability requires that all of the changes made to the database be permanent once a transaction is successfully completed.
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