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From: Georg Bauhaus <sb463ba@l1-hrz.uni-duisburg.de>
Newsgroups: comp.lang.ada
Subject: Re: Windows Ada database support.
Date: Wed, 8 Dec 2004 02:24:25 +0000 (UTC)
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Dmitry A. Kazakov <mailbox@dmitry-kazakov.de> wrote:
: On Tue, 7 Dec 2004 15:49:36 +0000 (UTC), Georg Bauhaus wrote:
: 
:> Dmitry A. Kazakov <mailbox@dmitry-kazakov.de> wrote:
:> 
:>: I think that this is a shortcoming of the very concept of a relational
:>: view. Relation is not an array. Period.
:> 
:> Who says that a relation is an array?
: 
: Nobody. The problem is that we need arrays, or more generally, ordered
: containers. This is the way the most people think about tables.

Hm. If at the DB level you ask,

SELECT S.key, T.foo, T.bar from S, T
WHERE (S.key BETWEEN 100 AND 200)
  AND T.foo = S.key
ORDER BY S.key

Then you have in Ada.Container terms,
   function Floor (Container : Map;
                   Key       : Key_Type) return Cursor;

   function Ceiling (Container : Map;
                     Key       : Key_Type) return Cursor;
where
   S.key >= 100  can be made the floor
and
   S.key <= 200  can be made the ceiling.


: They do not
: think about them in terms of relations.

You mean they do not think about the relations between records,
for example? Well, yes, but how could this be overcome using
another language? A fair amount of referential integrity can
be "extracted" from an ER diagram using standard means. If this
way of defining tables in a database is not standard, do you think
that another standard, Ada, is going to help?


: Why an application that need to store data, should care about that? Sorry,
: I still cannot understand it.

1/ other applications may (have to) modify your data without notice.
3/ storing data might take time. RDB or not, I need to know this
2/ you might need backups and secure storage. This is provided by
   good RDBMSs.

: Do you care much about ferromagnetism when
: you write a file onto the hard drive?

I certainly do. In particular when the disks are 5 years old
and not part of a well maintained RAID. ;-)


-- Georg