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Rick van der Lans

Welcome to my blog where I will talk about a variety of topics related to data warehousing, business intelligence, application integration, and database technology. Currently my special interests include data virtualization, NoSQL technology, and service-oriented architectures. If there are any topics you'd like me to address, send them to me at rick@r20.nl.

About the author >

Rick is an independent consultant, speaker and author, specializing in data warehousing, business intelligence, database technology and data virtualization. He is managing director and founder of R20/Consultancy. An internationally acclaimed speaker who has lectured worldwide for the last 25 years, he is the chairman of the successful annual European Enterprise Data and Business Intelligence Conference held annually in London. In the summer of 2012 he published his new book Data Virtualization for Business Intelligence Systems. He is also the author of one of the most successful books on SQL, the popular Introduction to SQL, which is available in English, Chinese, Dutch, Italian and German. He has written many white papers for various software vendors. Rick can be contacted by sending an email to rick@r20.nl.

Editor's Note: Rick's blog and more articles can be accessed through his BeyeNETWORK Expert Channel.

About two months ago, Pervasive Software asked me to write a whitepaper describing how well their popular PSQL database server supports Codd's twelve rules for relational databases.

For those not familiar with these rules, in 1985, E.F. (Ted) Codd, the founder of the relational model, defined a set of twelve rules for determining how well a database product supports the relational model. These rules make it possible to answer the question whether a particular product is a relational database server. They were urgently needed, because many vendors were labeling their products as relational, while they were not. So, the term relational became somewhat polluted and Codd wanted to fix and prevent this.

The study was a real trip down memory lane. It was a pleasure to reread all those articles and books written by Codd himself and those by Chris Date on, for example, updatable views. The work they did then, was brilliant. So much of what they wrote, is after so many years, still very true.

After studying Pervasive PSQL in detail, my verdict is that it scores a 10 (on a scale of 0 to 12). Nine rules are fully supported, two partially, and two not. Therefore, the overall conclusion is that PSQL is 83% relationally complete. This is an excellent score and puts PSQL in the list of most relational products.

Is it possible to be 100% relational? The answer is yes. Such products can be developed. In fact, there is one open source product that supports most of the rules: Alphora's DataPhor. However, the product is not (yet) a commercial success. In the same year when Codd introduced the twelve rules, he also wrote "No existing DBMS product that I know of can honestly be claimed to be fully relational, at this time." It looks as if this statement still holds for all the SQL products and probably for most database servers.

Note: Now that Pervasive and Actian have merged, maybe I should write a comparable paper for their Ingres and Vectorwise database server, and see which one is the most relational product.

Posted April 15, 2013 7:40 AM
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