Re: Concurrency in an RDB
Date: Fri, 22 Dec 2006 14:16:43 GMT
Message-ID: <fNRih.36184$cz.534424_at_ursa-nb00s0.nbnet.nb.ca>
paul c wrote:
> Bob Badour wrote: >
>> paul c wrote:
>>
>>> paul c wrote:
>>>
>>>> David wrote:
>>>>
>>>>> paul c wrote:
>>>>>
>>>>>> Marshall wrote:
>>>>>>
>>>>>>> On Dec 20, 3:13 pm, monaro..._at_gmail.com wrote:
>>>>>>>
>>>>>>>> Marshall wrote:
>>>>>>
>>>>>> ..
>>>>>>
>>>>>>>> Is English your second language?
>>>>>>>
>>>>>>> Wow, an insult in which you imply that I don't speak
>>>>>>> English very well. Isn't *that* original, and oh so relevant?
>>>>>>> ...
>>>>>>
>>>>>> Hey Marshall, your anglais is satisfactaire. it's standard technique
>>>>>> for newsgroup/"successful" hand-wavers to challenge an irrelevant
>>>>>> aspect
>>>>>> of the questioner's manner, ie., to try to change the subject.
>>>>>
>>>>> I have an interest in carefully analysing why people say what they
>>>>> say...
>>>>>
>>>>> Here are some possible motivations for why Dan posed that question...
>>>>>
>>>>> 1. Dan actually believes English is not Marshall's primary
>>>>> language,
>>>>> and the question was to be taken literally
>>>>>
>>>>> 2. Dan believes Marshall can speak English well, but thinks some of
>>>>> the NG readers are naive enough to read his question literally. This
>>>>> is a ploy to help bolster his argument by attacking Marshall's
>>>>> intelligence - perhaps because Dan thinks his argument isn't able to
>>>>> stand up on its own.
>>>>>
>>>>> 3. Dan used it as a literary device, as both an insult and to
>>>>> underscore what he regards as a discrepancy in Marshall's response.
>>>>>
>>>>> It seems to me that the third option is closest to the truth.
>>>>>
>>>>> You claim that the second option is in fact true. Do you stand by
>>>>> that
>>>>> claim, or do you in fact agree with me that the third option is
>>>>> closest
>>>>> and you are yourself using the analogous tactic that you "accuse" Dan
>>>>> of?
>>>>>
>>>>> David
>>>>
>>>> You can claim that I claim whatever you want. Doesn't make it so.
>>>> Here's a claim I admit - I claim that Christmas time is when lots of
>>>> directionless people (ie., the majority who have no substantial
>>>> inspiration on this topic or anything else) like to make lists of all
>>>> sorts. Unfortunate side-effect of the 20th century's emphasis on
>>>> universal so-called literacy. Suggest you send your list to the
>>>> local so-called newspaper.
>>>>
>>>> Here, in any season, I would rather hear an opinion, even an uninformed
>>>> one, on what it means to
>>>> Cheers,
>>>
>>> Let me re-ask that: what does it mean to project A from a relation
>>> that has two attributes, one A of some specified/understood type and
>>> the other B whose type is the same as the relation (A,B).
>>
>> It means the same as projecting A from a relation (A,B) where B is an
>> integer. In the projection, B and its data type are irrelevant.
> > I am guessing that one meaning you have in mind is that "it means the > same as projecting from a relation (A,B) where B is an intgeger and > (A,B) is an integer?
What I am saying is: When you project onto A, the data type of B is
mostly** irrelevant. Likewise, when you project onto B, the data type of
A is mostly irrelevant.
The fact that you have a recursive data type definition has no effect on
project or join or restrict or union or intersect or difference etc. The
values identified as B are simply values.
Assuming:
A = { a1, a2, a3, a4, a5 }
Given relation R{a in A,b in B}: /* Using C-style comments */
R = { { a1, { a2, { a3, {} } } } /* a=a1, b={ a2, { a3, {} } */
, { a4, { a3, {} } } /* a=a4, b={ a3, {} } */
, { a5, { a2, { a3, {} } } } /* a=a5, b={ a2, { a3, {} } */
Project R onto R1=R{A}:
R1 = { { a1 }, { a4 }, { a5 } }
Project R onto R2=R{B}:
R2 = { { a2, { a3, {} } }, { a3, {} } }
B = { {a,b} | a in A and b in B }
- I say "mostly" irrelevant because the predicate for the projected relation still makes reference to B in the sense of "A where exists some B".