Re: A simple notation, again
From: Brian Selzer <brian_at_selzer-software.com>
Date: Tue, 17 Jul 2007 21:19:13 GMT
Message-ID: <lnani.39745$Um6.679_at_newssvr12.news.prodigy.net>
>> "David Cressey" <cresse..._at_verizon.net> wrote in message
>>
>> news:o4Lmi.4051$fj5.2089_at_trnddc08...
>>
>> > Using the notation [A B C] for <NOT> (A <AND> B <AND> C), etc.
>>
>> > The following [ A [B]] means "A implies B" for Boolean algebra.
>> > What
>> > is
>> > the corresponding thing for Relational Algebra?
>>
>> > Also, I'm trying to come up with a bracket notation for a "literal
>> > relation", like literals for simple datatypes like numbers and
>> > character
>> > strings.
>>
>> > I'm toying with this:
>>
>> > [["David" "Cressey" 1]
>> > ["Marshall" "Spight" 2]
>> > ["Bob" "Badour" 3]
>> > ["Jan" Hidders" 4]]
>>
>> How about something like this
>> {(Last, First, Num) :
>> ("David", "Cressey", 1),
>> ("Marshall", "Spight", 2),
>> ("Bob", "Badour", 3),
>> ("Jan", "Hidders", 4)}
True, but order is imposed here simply to associate each element of each tuple with its designation. It is used only as a shorthand. Received on Tue Jul 17 2007 - 23:19:13 CEST
Date: Tue, 17 Jul 2007 21:19:13 GMT
Message-ID: <lnani.39745$Um6.679_at_newssvr12.news.prodigy.net>
"Cimode" <cimode_at_hotmail.com> wrote in message news:1184659859.447753.106610_at_i38g2000prf.googlegroups.com...
> On Jul 16, 7:05 pm, "Brian Selzer" <br..._at_selzer-software.com> wrote:
>> "David Cressey" <cresse..._at_verizon.net> wrote in message
>>
>> news:o4Lmi.4051$fj5.2089_at_trnddc08...
>>
>> > Using the notation [A B C] for <NOT> (A <AND> B <AND> C), etc.
>>
>> > The following [ A [B]] means "A implies B" for Boolean algebra.
>> > What
>> > is
>> > the corresponding thing for Relational Algebra?
>>
>> > Also, I'm trying to come up with a bracket notation for a "literal
>> > relation", like literals for simple datatypes like numbers and
>> > character
>> > strings.
>>
>> > I'm toying with this:
>>
>> > [["David" "Cressey" 1]
>> > ["Marshall" "Spight" 2]
>> > ["Bob" "Badour" 3]
>> > ["Jan" Hidders" 4]]
>>
>> How about something like this
>> {(Last, First, Num) :
>> ("David", "Cressey", 1),
>> ("Marshall", "Spight", 2),
>> ("Bob", "Badour", 3),
>> ("Jan", "Hidders", 4)}
> You imply order (adjacency) when relation attributes should not be > subjected to any.... > >
True, but order is imposed here simply to associate each element of each tuple with its designation. It is used only as a shorthand. Received on Tue Jul 17 2007 - 23:19:13 CEST