From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00 autolearn=ham
	autolearn_force=no version=3.4.4
X-Google-Thread: 103376,86a457a80a9f4412
X-Google-Attributes: gid103376,public
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news1.google.com!news4.google.com!news.germany.com!news.belwue.de!newsfeed.arcor.de!newsspool4.arcor-online.net!news.arcor.de.POSTED!not-for-mail
Newsgroups: comp.lang.ada
Subject: Re: Generic Collection
From: Georg Bauhaus <rm.tsoh+bauhaus@maps.futureapps.de>
In-Reply-To: <1178652593.006083.173150@l77g2000hsb.googlegroups.com>
References: <1178652593.006083.173150@l77g2000hsb.googlegroups.com>
Content-Type: text/plain
Content-Transfer-Encoding: 7bit
Message-ID: <1178658022.9164.17.camel@kartoffel>
Mime-Version: 1.0
X-Mailer: Evolution 2.10.1 
Date: Tue, 08 May 2007 23:00:23 +0200
Organization: Arcor
NNTP-Posting-Date: 08 May 2007 23:00:12 CEST
NNTP-Posting-Host: abc060a7.newsspool4.arcor-online.net
X-Trace: 
 DXC=[Q>6@SbXad:RLigj];iP=84IUK<Cl32<14Fo<]lROoR14nDHegD_]R54NnAmBHB<P1N[W<lHX`=B4\6BhD5G6\i<^RWD1ia[nN?
X-Complaints-To: usenet-abuse@arcor.de
Xref: g2news1.google.com comp.lang.ada:15659
Date: 2007-05-08T23:00:12+02:00
List-Id: <comp.lang.ada>

On Tue, 2007-05-08 at 12:29 -0700, andrew wrote:

> I cannot say for sure if the "is a" relations aren't entirely
> artificial.  It seems to me it would work either way.  The difference
> for me is that I cannot visualize the composition you mentioned.

As you noted, I meant that "a tuple is a collection of attributes"
doesn't necessarily imply inheritance relationship; TUPLE doesn't have
to inherit from a type COLLECTION_OF_ATTRIBUTES.

I think there are various possibilities; RDB2 (below RDB) shows
types that have components of other types (that is, are composed :-)
but are otherwise unrelated.
Package RDB desclares "is a" relations in the sense you describe
by making the DB types be "a collection of" objects of "smaller"
types.


> So what you are saying is that the type Item in my example is the
> parameter you are talking about?

Erh, I guess so.

with Ada.Containers.Hashed_Sets;
with Data;

package RDB is

   use Ada;

   type DP is access Data.T'class;
   function compare(a, b: DP) return BOOLEAN;
   function hash(element: DP) return Containers.HASH_TYPE;


   subtype ATTRIBUTE is DP;

   package Attributes is new Containers.Hashed_Sets
     (ELEMENT_TYPE => ATTRIBUTE,
      hash => hash,
      equivalent_elements => compare);


   subtype TUPLE is Attributes.SET;
   function hash(element: TUPLE) return Containers.HASH_TYPE;


   package Tuples is new Containers.Hashed_Sets
     (ELEMENT_TYPE => TUPLE,
      hash => hash,
      equivalent_elements => Attributes."=",
      "=" => Attributes."=");


   subtype TABLE is Tuples.SET;
   function hash(element: TABLE) return Containers.HASH_TYPE;


   package Tables is new Containers.Hashed_Sets
     (ELEMENT_TYPE => TABLE,
      Hash => hash,
      equivalent_elements => Tuples."=",
      "=" => Tuples."=");

   -- ...

end RDB;


with Ada.Containers.Hashed_Sets;
with Data;

package RDB2 is

   use Ada;

   type DP is access Data.T'class;
   function compare(a, b: DP) return BOOLEAN;
   function hash(element: DP) return Containers.HASH_TYPE;


   subtype ATTRIBUTE is DP;

   package Attributes is new Containers.Hashed_Sets
     (ELEMENT_TYPE => ATTRIBUTE,
      hash => hash,
      equivalent_elements => compare);

   type TUPLE is
      record
         -- ...
         columns: Attributes.SET;
      end record;
   function compare(a, b: TUPLE) return BOOLEAN;
   function hash(element: TUPLE) return Containers.HASH_TYPE;


   package Tuples is new Containers.Hashed_Sets
     (ELEMENT_TYPE => TUPLE,
      hash => hash,
      equivalent_elements => compare);


   type TABLE is
      record
         -- ...
         rows: Tuples.SET;
      end record;
   function compare(a, b: TABLE) return BOOLEAN;
   function hash(element: TABLE) return Containers.HASH_TYPE;


   package Tables is new Containers.Hashed_Sets
     (ELEMENT_TYPE => TABLE,
      Hash => hash,
      equivalent_elements => compare);

   type SCHEMA is
      record
         -- ...
         relations: Tables.SET;
      end record;


end RDB2;