Re: cdt

From: mAsterdam <mAsterdam_at_vrijdag.org>
Date: Sun, 06 Jun 2004 16:21:28 +0200
Message-ID: <40c32861$0$559$e4fe514c@news.xs4all.nl>

Alan wrote:

> Laconic2 wrote:

>>Perhaps the problem lies in the word "implicit", in the term "implicit
>>meaning".  Perhaps what is implicit is subject to misinterpratation.

>
> Not if you know the difference between implicit and explicit, which you have
> provided by example, below. Implicit is implied, explicit is expressed.
> Implicit is correct in this case. I'm fairly sure Drs. Elmasri and Navathe
> carefully considered which word to use, and that their editor reviewed it
> somewhere during the process of creating three editions of the book. Try,
>
> Known facts that can be recorded and have _an implied_ meaning.
>
> They're not explicit until after they've been recorded (or stated, i.e.,
> expressed).
>

>>Back in the days before databases,  when COBOL programmers stored data in
>>records in files,  the records had an "implicit" record definition.  The
>>COBOL programmer needed to include the correct record definition in the
>>program in order to read the data.  By including the data definitions in
>>By including the data definitions in the
>>schema, and putting the schema in the database, the definitions were made
>>"explicit" rather than "implicit".

Column names, table names hint at meaning, they do not really define.

It does not help rephrasing this in relational terms: The names of attributes and relational variables don't do a better job at defining. The meaning of the propositions conveyed by the tuples is supposed to be explained by the *external* predicate (3rd manifesto, 1st edition). "external" suggests that the authors do not think of the predicate as being part of the database - but I can't check this as I don't have the book here. The "definitions" in the schema only serve to associate the structure of the relation body with the relation header. Received on Sun Jun 06 2004 - 09:21:28 CDT