Re: Generic Collection

[andrew <andrew.carroll@okstate.edu>]

On May 8, 4:00 pm, Georg Bauhaus <rm.tsoh+bauh...@maps.futureapps.de>
wrote:
> 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;

RDB2 looks good to me and is pretty close to what I had in mind.

I think I finally get what you were saying about inheritance.  Before
I posted the topic I was thinking about the design and I just wrote
down the "table is a collection" as part of sentence.  In my mind I
was thinking of a variable declaration:

table: collection;
tuple: collection;
schema: collection;

and so I posted my question.