Re: Queries and OO

From: Dmitry A. Kazakov (mailbox_at_dmitry-kazakov.de)
Date: 01/16/05 

Date: Sun, 16 Jan 2005 17:59:59 +0100

On 16 Jan 2005 07:28:23 -0800, frebe wrote:

> Robert C. Martin wrote:
>>>After some debates at this forum I have made the conclusion that the
>>>concepts of queries does not exists within OO.
>>
>> True. OO is a set of tools and techniques for managing source code
>> dependencies. It has nothing to do with databases.

I line with Robert here.
 
> I didn't say anything about databases. I asked about the querying
> objects.

I'd say that querying is rather about some specific implementation than
modeling. This kind if implementation forces you to have a very flat type
hierarchy with a limited set of available operations. It might be OK for
some applications and absolutely unsuitable for others. Of course it does
not mean that a query language cannot be complete (in Turing sense etc),
just it is a very low-level abstraction as compared with OO approach.

>> The safest way to think about this is to separate the concept of OO
>> and DB completely. OO has nothing to do with databases, and databases
>> have nothing to do with OO.
>
> Isn't queries something you may need even if you don't use a database?

I might need no queries even if I do use a database. For example, all
queries could be locked in low-level implementation package used for
interfacing DB. The rest might be completely unaware of them.

>> When you see the word "object" used in
>> reference to database like things (e.g. OQL, OODB) it does not refer
>> to the same "object" when you see it used in reference to programming
>> like things (e.g. OOP, OOD, inheritance, polymorphism).
>
> But classes/objects can be used to model almost anything in the "real
> world". And if databases exists in the "real world", it must be
> possible to describe them as a structure of objects, or?

Probably yes, but it would be rather uninteresting objects. What could be
so intriguing in a set of tables? 

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de

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