Re: A simple notation, again

From: mAsterdam <mAsterdam_at_vrijdag.org>
Date: Sun, 22 Jul 2007 22:27:53 +0200
Message-ID: <46a3bd80$1$336$e4fe514c@news.xs4all.nl>

David Cressey wrote:

> Brian Selzer wrote:
>> David Cressey wrote:

>>> 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)}
>>

>>> This would represent a relation of order 3 and cardinality 4.
>>>
>>> What I don't like about this is that the binding between attribute
>>> values and attribute names is by position
>>> rather than by name, and in fact the attribute names don't even
>>> appear here. That's unacceptably bad. The symmetry is appealing, but
>>> it clearly needs improvement.
>>>
>>> Does tutorial D have a way of laying out a relation as an explicit
>>> literal character string?

> 
> I like the colon.  I'd like to stay within the square 
> bracket notation, if possible.

</lurk>
Your call. Hey! It is your notation.

What about the relation name in the literal?

[Person[ ...                            ?

[[ ... would be an anonymous relation ?

colons are also used to denote types.

Combining an relationname and both colons would make the literal look like:

[Person[Last:doublequotedstring First:doublequotedstring Num:decimalnumber]:

["David" "Cressey" 1]
["Marshall" "Spight" 2]
["Bob" "Badour" 3]
["Jan" Hidders" 4]]

... though I would prefer commmas like in Brian's version, avoiding the need for CamelCasing or lots of underscores.

[Person [

   Last:doublequoted string,
   First:doublequoted string,
   Num:decimal number
   ]
  :

  ["David", "Cressey", 1]
  ["Marshall", "Spight", 2]
  ["Bob", "Badour", 3]
  ["Jan", Hidders", 4]

] Received on Sun Jul 22 2007 - 15:27:53 CDT