Re: teaching relational basics to people, questions
Date: Sat, 28 Nov 2009 05:06:40 GMT
Message-ID: <Ad2Qm.55460$PH1.49121_at_edtnps82>
compdb_at_hotmail.com wrote:
> On Nov 26, 2:19 am, "Mr. Scott" <do_not_re..._at_noone.com> wrote:
...
...
>> The logical connective should be IFF rather than AND. The
>> difference is subtle, and may at first glance appear problematic since IFF
>> is true whenever none of its operands are true, but under the closed world
>> assumption, the only atomic formulas that are ever represented in the
>> database are those that are supposed to be true, so there is no harm in
>> choosing IFF over AND. The main reason I think the connective should be IFF
>> rather than AND involves deletes. While inserting a row effectively asserts
>> that all of the atomic formulas represented by the row are true
> ... > > , regardless
>> of the whether the logical connective is IFF or AND,
> ...
I believe IFF as well as AND can be expressed with NAND. So, what is the argument?
The only thing I wonder about is why constraints must be truth-valued. I'd rather they were allowed to have relation values other than dee and dum. Seems the only way to allow defaults/mandatory tuples without introducing some other concept. Received on Sat Nov 28 2009 - 06:06:40 CET