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Open Source Database Management Systems
By Craig S. Mullins

The rapid acceptance and media glare surrounding Linux has enlivened the Open Source community. The term "open source" refers to software that users are free to run, copy, distribute, study, change and improve. Often "open source" is interpreted to mean free software. This is understandable, but the open source concept of free is closer to liberty than to no charge. Open Source software adheres to the following beliefs:

• Users are free to run the program, for any purpose.
• Users are free to inspect the actual source code of the program to determine how it works.
• Users are free to modify and adapt the software to their specific needs.
• Users are free to redistribute copies to whomever.
• Users are free to release their code improvements to the public, so that the whole community benefits.

Linux is an open source operating system based on UNIX. Companies like Red Hat and Caldera have become overnight sensations by packaging and providing support for Linux. Even established companies are embracing Linux: Corel distributed a version of Linux and has ported its Office suite to Linux and IBM has even announced a version of Linux that runs on their System 390 mainframe.

But operating systems are not the only programs available as open source. There are several open source database management systems that are beginning to make some waves.

PostgreSQL began at the University of California, Berkeley as the second generation of University Ingres. The Ingres code was enhanced into a commercial product by Relational Technologies. Relational Technologies became Ingres Corporation, which was purchased by ASK Corporation, which was then purchased by Computer Associates.

Ingres was enhanced at the University of California, Berkeley, too, eventually turning into the second generation Postgres. Both Ingres and Postgres were the brainchildren of Michael Stonebraker, founder of Illustra and now with Informix. PostgreSQL is also commonly referred to simply as Postgres and I will use the two interchangeable in this article.

The PostgreSQL DBMS is released under a Berkeley-style license, which, unlike the general public license used by Linux (for more information http://www.fsf.org/copyleft/gpl.html), allows companies to take the software and add proprietary extensions. With Linux, by contrast, companies or individuals are required to publicly release any changes made if they choose to distribute the software.

Postgres is a fully functional object/relational database management system. PostgreSQL version 7.0 is compliant with the entry-level SQL92 standard. Full compliance with the SQL92 standard should be available in the upcoming 7.1 release. Postgres supports multiple types of indexes, a very complete set of data types, row-level locking, triggers, constraints, and most of the features required of a robust relational database server today.

Great Bridge LLC (http://www.greatbridge.com), a subsidiary of media company Landmark Communications, is looking to become the Red Hat of the Postgres world. Red Hat was one of the first companies to package, distribute, and support Linux, and had a very successful IPO in 1999. Great Bridge is hoping that the next wave of the open-source software trend will be database management systems.

Great Bridge hopes to popularize Postgres and profit from distributing the Postgres software and supporting Postgres users. It will be interesting to see how successful Great Bridge can be. The RDBMS game is quite different than the operating system game. The main players in the RDBMS arena are IBM, Oracle, and Microsoft. Most organizations have implemented one or more instances of these three major vendor’s products. Changing RDBMS vendors is not a simple task because the features and syntax of each product differ, requiring costly and time-consuming application changes.

Another hurdle for Great Bridge to clear is the failure of Ingres to capture and hold a large percentage of the market. Although Ingres is still marketed and sold by Computer Associates, it is not one of the major RDBMS players today. Those with a long memory may consider Postgres to be a commercial failure because of Ingres’ failure to capture market share.

Finally, Michael Stonebraker used Postgres as the basis for the Illustra object/relational database server. Illustra was the first commercial object/relational product and revolutionized the market for storing large multimedia objects in relational databases. Informix acquired Illustra and used the Illustra technology as the basis for Informix Universal Server. Some users may wish to purchase this technology from Informix instead of going the open source route with Postgres and Great Bridge, believing that a commercial company the size of Informix will be better suited to support and extend their product.

But many of the users who embraced Linux as an alternative operating system to the many flavors of commercial UNIX and the Windows platforms offered by Microsoft may view Great Bridge Postgres as just the RDBMS for their Linux server. And as the market share for Linux grows, so may Postgres. Only time will tell.

InterBase is another option for users desiring an open source RDBMS. InterBase is the RDBMS formerly owned by Inprise, which is the company formerly known as Borland. Borland acquired InterBase Software Corporation, the original creators of InterBase. Borland had a knack for taking successful database software and allowing it to unravel. Witness not just InterBase, but also dBase (now a separate company, independent from Inprise) and Paradox (now owned by Corel).

Inprise decided to take the open source route with InterBase in January 2000. The source code for InterBase Version 6 has been published and is available as open source. However, Inprise also continues to sell and support InterBase Version 5.6 through its normal distribution channels.

In February 2000, Inprise recreated InterBase Software Corporation to manage the InterBase open source project. The InterBase RDBMS is freely available to users under the terms of the InterBase public license, which is based on the Mozilla Public License. Complete details are available at http://www.interbase.com/.

So, InterBase the DBMS is true open source software. You can obtain and modify the source, under the stipulation that you share your modifications with others. However, the InterBase license is controlled by InterBase the company, and only they can modify that license.

Moving InterBase to the open source model was a wise course of action because the competition from Oracle, IBM, Informix, Sybase, and Microsoft was fierce, and InterBase has a relatively small market share compared to the leaders. As an open source RDBMS, InterBase may have some new life breathed into it.

MySQL is a true multi-user, multi-threaded SQL database server. It is available as a free download from http://www.mysql.com, but it is not technically an open source DBMS. You do not get access to the source code, and therefore are not able to modify it. Additionally, you must pay for a license if you sell MySQL, charge for administering a server, or include MySQL as a component of a distribution. Furthermore, MySQL is free of charge on UNIX and OS/2 platforms only. For Windows platforms you must purchase a software license. A free, slower version of MySQL is available for Windows platforms on a 30-day trial period.

MySQL is a good alternative to high-cost, commercial DBMS products for small- to mid-range database servers and applications. But it is not open source software.

If you are looking for a low cost alternative to the traditional relational DBMS vendors, one of these open source or low-cost relational database servers may be just the ticket for you. But be aware that these alternatives will usually lag behind Oracle, DB2, and Microsoft SQL Server in terms of features, functions, and performance. Even more problematic is the lack of database administration tools like schema change managers, SQL tuning, and performance monitors. Without these tools, administration will probably be more difficult than you are used to. But if cost is an issue, your database size is manageable, and usage is low to medium, Postgres, InterBase, or MySQL might be viable options for you.

From Database Trends, July 2000.
 
© 2000 Craig S. Mullins,  All rights reserved.
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