The Rise of Relational Databases

Large-scale computer applications require rapid access to large amounts of data. A computerized checkout system in a supermarket must track the entire product line of the market. Airline reservation systems are used at many locations simultaneously to place passengers on numerous flights on different dates. Library computers store millions of entries and access citations from hundreds of publications. Transaction processing systems in banks and brokerage houses keep the accounts that generate international flows of capital. World Wide Web search engines scan thousands of Web pages to produce quantitative responses to queries almost instantly. Thousands of small businesses and organizations use databases to track everything from inventory and personnel to DNA sequences and pottery shards from archaeological digs.

Thus, databases not only represent significant infrastructure for computer applications, but they also process the transactions and exchanges that drive the U.S. economy..........

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Relational Databases

by Anthony and Hala Awtrey

One of the most powerful tools computers give us is the ability to store and search data. Early applications stored data for programs in files and used indexes to search the files for particular bits of data. These programs didn't fare very well on networks because there are problems with more than one computer trying to update data in a file simultaneously. This fact and the lack of standard database structure and command syntax encouraged the creation of the networked relational database.

When you write a program and want to be able to manipulate and search data you often have to construct the data files and the code to perform the manipulation and searches. This is a time consuming task and if you are developing many different applications you have to reinvent the data handling routines for every job. By removing the database functions such as file management, indexing, searches and simultaneous data access, you speed up development of applications and allow for these specialized database programs to become highly optimized and scalable.

What is a database
A database is simply organized data. A database contains tables which are basically descriptions of types of data. Tables in turn contain records which is the actual data......

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RDBMS - Relational Database Management Systems

By Christopher Browne

Database Classifications

There are several ways of classifying the database systems available for Linux:

• Based on "freeness." - There are commercial packages (sold for a price), and there are free software database systems (that do not cost anything to acquire). This is fairly closely correlated to availability of usable source code, which is another legitimate interpretation of "freeness."

• Compatibility/Means of Functioning -

1. xBASE - This is traditionally a "PC" oriented system, of which the first version was known as Vulcan, and ran under CP/M . It was later renamed dBase, and later versions and competitors have followed.
   

   The system model generally involves data structured in a dual fashion similar to ISAM databases with "data" files containing data, and "index" files containing index information. Applications access data directly by reading the files. Newer versions have a network locking system to manage contention for files and/or records if multiple users try to access data simultaneously, but there is still contention inherent in that many programs are accessing the same files simultaneously.
   

   More modern systems use "extent-based" allocation systems to better support the handling of tuples of varying sizes.

2. SQL - Structured Query Language - Ingres was the progenitor of the modern "query language," with its QUEL query language; a similar query language was then designed that we now know as SQL. SQL is arguably inferior to QUEL, as QUEL had a syntax that is simultaneously simpler and more powerful than that of SQL.
   

   The system model typically involves there being a central database manager "engine" or "process;" application programs do not have direct access to the data. This allows data to be relatively protected from corruption/misuse by rogue processes.

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Dilip's Brief Introduction to Relational Databases

cs.unc.edu

Lesson Overview

As part of the spring 1998 Advanced Java Course at UNC, I am giving the first seminar intended to introduce the audience to relational databases and give a tutorial on Microsoft Access. This lecture precedes one by Wen Zhang and Ganesh Srivinas about connecting to a database from java, and a final database lecture by Will Sexton and Rich Thornett about the "JDBC".

We start off quickly looking at the notion of "database" and consider the simple relational database model of tables with tuples (rows) and attributes (columns). A popular way to design a database is through ER diagrams, and we look at a sample diagram. I hope that you won't get bogged down when we discuss the relational algebra, set theoretic notions that the relational model is based upon. Though it is important to have some basic understanding of the relational algebra, in practice most users take advantage of a higher level language for retrieving information from a database, and we look at SQL (Structured Query Language) as a common example. Finally, we motivate the use of Microsoft Access, a popular relational database system, and follow-on with a detailed tutorial on how to use Access.

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