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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