Re: On view updating

From: mAsterdam <mAsterdam_at_vrijdag.org>
Date: Sun, 26 Sep 2004 09:45:57 +0200
Message-ID: <415673b6$0$25965$e4fe514c@news.xs4all.nl>

Alfredo Novoa wrote:

> mAsterdam wrote:

>>The consequence is that many lengthy misunderstandings
>>can be avoided by immediately giving a clear
>>definition of some crucial terms whenever used
>>in a discussion which goes beyond one of those groups.
>>Define it for the discussion at hand.
>>My hope is that new, more broadly used definitions
>>will arise.

>
> I agree. Fortunately we have dictionaries and institutes of standards.

They *do* help. There are topics though where there are competing dictionaries though, one group takes one set of dictionaries etc...

>>My statement asserts several things in one go,
>>but most importantly: that 'type' is one of the
>>words that has its meaning bend and twisted
>>(jargonised) subtly differently in different
>>groups. I call it a non-problem, because I suspect
>>the jargon differences cover up some real,
>>perception of subjectmatter related (instead of
>>just the labeling), interesting problems.

>
>
> My obvious sugestion is that we should resort to the authoritative
> references:
>
> http://www.nist.gov/dads/HTML/abstractDataType.html

Heh. It has the definition I am currently questioning. It smells.

But yes. Thing is: if you want to challenge those definitions you'll have to be explicit about it.

>>>They are intended to be shorthands for expressions, but they are not
>>>syntactic shorthands because they are database objects. Views exist in
>>>the database catalog.
>>
>>Syntactic shorthands cannot exist within the database catalog?

>
> No, it makes no sense. A syntactic shorthand is only an alternative
> and shorter way to say something, and not an alternative way to
> achieve a desired result.
>
>

>>>Both groups of statements have different semantics therefore a view is
>>>not a syntactic shorthand.
>>
>>If the deletion of 'r where a > 10' is a common thing to do,
>>then var v makes database A easier in use than database B.

>
>
> Indeed, not all shorthands are syntactic.

Ah... ok. Shorthand yes, if you really want to see it that way, but syntactic no. Maybe things like this is why some distinguish a sigmatic layer between syntactic and semantic. I could not find a good reference to look into that, though.

>>Assuming var r has the same semantics and values in both databases,
>>both databases reflect the same facts.
>>This is true before and after the deletes.

>
> Indeed, but the statements have different meanings, and syntactic
> shorthands only affect to the syntax, and never to the meaning.

Yep.

> For instance:
>
> a := a + 5;
>
> is not a syntactic shorthand for this:
>
> for i := 1 to 5;
> a := a + 1;
>
> The result is the same, but we are not saying the same.

IOW: semantically different, pragmatically the same.

>>>delete a union b;
>>>
>>>or
>>>
>>>var r relation { a integer }
>>>    key { a }
>>>    foreign key { a } references a union b;  
>>
>>This puzzles me. From 'delete a union b;' I took the suggestion
>>that a and b where both relational variables.

>
> Yes.
>

>>In the second 
>>statement a is a declared integer in the first line,
>>and what is a in the tail of the 3rd line of the second statement?

>
>
> The same relation variable as in 'delete a union b'.
>
> In relational databases is frequent to have relvars and attributes
> with the same name,
> but I should have used a different name, sorry.

Heh. Yes, that helps in examples. Thank you. Received on Sun Sep 26 2004 - 02:45:57 CDT