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Date defends relational model

Chris Date, a renowned proponent of the relational model, takes on SQL, XML and all things object-oriented in a fiesty keynote address at the DAMA symposium this week.

LOS ANGELES -- Chris J. Date has said it before, and he said it again at the DAMA International Symposium's opening keynote.

"Let us vow to never say 'flat tables' again," Date said. Yesterday, the crowd erupted into applause for Date and his attempts to "edify and amuse" his audience.

The biggest problem about SQL is that it does not implement the relational model.
Chris Date
relational DBMS expert

Date is the author of 22 influential data management-related books, including "An Introduction to Database Systems," now in its eighth edition. His keynote kicked off the 16th annual DAMA (Data Management Association) International Symposium this week.

Having spent decades as a staunch proponent of relational theory, Date tells database professionals that seemingly harmless phrases, such as flat tables, have added to the misconceptions that surround the relational model.

Date began his presentation by describing a sort of wall that encloses the place Date's friend and fellow relational theorist Hugh Darwen calls "Relational Land."

"Most people look for 'Relational Land' but only see the wall," Date explained. "They see problems and assume they are relational problems, but it is the wall that is the problem -- it is a barrier to communication."

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The relational model

DBMS performance

Among the barriers to the relational model, Date said, is the Structured Query Language (SQL).

"The biggest problem with SQL is that it does not implement the relational model," Date said, and named NULLs as a particular pet peeve.

"NULLs are an over-simplistic solution to a complicated problem," he said, disagreeing with his mentor Tedd Codd, the inventor of the relational model. "Codd was the only one who understood the relational model and he thought NULLs were a good idea."

Best-selling author Joe Celko, who says he "built a career on disagreeing with Chris Date," admits there are some things about SQL that could use improving.

For instance, Celko said he wishes the wild card symbol were not an underscore, now that laser printers are so prevalent. But overall, he said, SQL is logical, and as for NULLs, he sees no way around their use.

"The idea that you will always know everything is arrogant," Celko said.

Date reserved his harshest criticism for the competition, namely object-oriented and XML-based DBMSs. Calling them "the latest fashions in the computer world," Date said he rejects the argument that relational DBMSs are yesterday's news. Fans of object-oriented database systems "see flaws in the relational model because they don't fully understand it," he said.

Date also said that XML enthusiasts have gone overboard.

"XML was invented to solve the problem of data interchange, but having solved that, they now want to take over the world," he said. "With XML, it's like we forget what we are supposed to be doing, and focus instead on how to do it."

Craig S. Mullins, the director of technology planning at BMC Software and a expert, shares Date's opinion of XML. It can be worthwhile, Mullins said, as long as XML is only used as a method of taking data and putting it into a DBMS.

But Mullins cautioned that XML data that is stored in relational DBMSs as whole documents will be useless if the data needs to be queried, and he stressed Date's point that XML is not a real data model.

"There has been over enthusiasm surrounding XML. It has been hyped and everyone thinks it will infiltrate everything," Mullins said. "But if it infiltrates everything, then we've got problems everywhere."

As for the object-oriented DBMS, neither Mullins nor Date sees it as a threat to the RDBMS.

They both rejected the familiar analogy that object-oriented fans use. That is, with relational DBMSs, every time you want to process an object, you have to assemble it, which is the same as having to take your car apart in order to park it, and then assemble it every time you need to drive it.

Anyone who uses that analogy, Date said, displays a "lack of understanding of the difference between the logical and physical model." The use of the terms "flat tables" or "2D tables" to describe data stored in a relational database is wrong, he added.

When asked if the relational model was implemented soundly in today's systems, Craig Mullins' instant reply was "no," but he doesn't think the situation is as bad as Date says it is.

"We're doing production work and delivering value," Mullins said. "Isn't that what it is all about?"

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