Re: Extending my question. Was: The relational model and relational algebra - why did SQL become the industry standard?
Date: 3 Mar 2003 23:10:12 +0100
Lauri Pietarinen wrote:
>Jan Hidders wrote:
>>Well, your specific example involves recognizing that duplicate
>>elimination is not necessary in the view. That was something that was
>>researched as (relatively) recently as 1994:
>OK, point being that if SQL had not had duplicates from the start the
>motivation for such research would have been much stronger, and we would
>have got results sooner.
Could be, but note that this would then be because you made things *harder*
for the implementors and forced them to think about these issues.
>Meaning that "you can do more optimisations with set's"?
Meaning that in this case you might be right that for this particular query
the bag-based approach makes optimization a bit harder. However, after
giving it a bit more thought I doubt that even this is true. The problem is
just as difficult in a set-only as in a bag-based approach. In both cases
you can optimize a join followed by a project that projects out a certain
table by using only the index for the "invisible" table.
>>>would claim that the SQL-mode of thinking is hindering us from achieving
>>>this. And this (in my view) is ultimately Date's criticism of Hector
>>>Garcia-Molina, Jeffrey D. Ullman, and Jennifer Widom, DATABASE SYSTEM
>>Is he really criticizing this book? I don't get that impression from the
>>"double trouble" article on dbdebunk.
>No? At least he criticises some parts of it, or do you disagree?
Ah, wait, I hadn't really seen the appendix in part II. It's really Chris Date at his worst. After reading such nonsense it always takes me a day or two to take him serious again. For starters he seems to miss the essential point that the presented algebra is an internal algebra. When I read his remark about "classical relational algebra" I can only conclude that he is the one who doesn't know the literature. On all the conferences I have been I have heard this phrase used and everybody knew exactly what it meant. But no, Chris Date is going to explain to everyone what these words really mean. I can only describe that as hubris.
- Jan Hidders