SQL, XML, and the Relational Database Model

Kardamon writes "In an article on DBAzine, Fabian Pascal writes that SQL is not a good representation of the relational model, and is afraid the situation will get worse with XML and XQUERY. An overview of some of the reactions on the positions Pascal and also C.J. Date take on this issue is given in this article over at SearchDatabase.com by Sara Cushman."

Comments

Re:"NULLS are bad." quote

[MattRog]

To those not "in the know" here's some further clarification:

"The use of the terms "flat tables" or "2D tables" to describe data stored in a relational database is wrong, he added."

Basically what I take from this is that the table (e.g. SELECT * FROM foo) is simply a convenient logical representation of a stored relation. That is to say, foo can be implemented by the DBMS as a linked list, a tree, any data structure. The problem is that current SQL DBMS products do NOT do this and so we have the associated performance problems with normalized schemas. If the DBMS was truly a RDBMS then it could optimize the physical storage to improve performance.

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?"

The question is not "Are current SQL systems providing value" because certainly they are. They overthrew the hierarchic DBMS products for good reason - they were better. The real question is "Are the current SQL systems providing all the value they can". One can simply look at the wide array of DBMS offshoot products like XML DBMS, so-called "Multivalued DBMS" etc. to know that there are significant limitations of SQL products - ones which Date/Pascal/Darwin stress are not limitations of the Relational Model but merely these SQL products. To put words in their mouth, but I don't think they'd disagree at my summation, they'd suggest that if someone were to implement a Truly Relational Database Management System that these other products would quickly become obsolete.

Error: User doesn't know how to use program.

[LostCluster]

Most of the problems that I've seen with SQL commands that are more complex than they really should be are a result of mistaken assumptions made during the design phase of the database. As a result, extra tables get added late, and therefore create new "features" that code then has to be revised to take advantage of...

XML's going to be no better in this area. Mistakes made during the design phase will always come back to haunt while implementing and using the system. If a single query can't return the results desired, then that should have been thought of while designing the tables of the DB. Trying to get a query to specify "All things that are red" like Pascal suggests is only going to work if all objects implement the "color" property the same way. If somebody uses CMYK, somebody else uses RGB, and a third uses Play-Doh color names, it's still gonna be a mess that requires code to figure out who really matches whom.

I don't see how this "new model" fixes the real problems with working with SQL between databases that weren't designed to work with each other.