Re: Object oriented database
Date: Mon, 03 Nov 2008 11:49:28 -0400
Walter Mitty wrote:
> "David BL" <davidbl_at_iinet.net.au> wrote in message
>>On Nov 2, 8:40 am, JOG <j..._at_cs.nott.ac.uk> wrote: >> >>>These are the people who are worth discussing data models with >>>because, well, they realise OO isn't one, and they have built another >>>on top as best they could within its constraints. >> >>I agree that OO isn't a data model. However, this depends on >>sufficiently narrow definitions of OO and data. The definition >> >> data = information in a form suitable for machine processing >> >>doesn't seem narrow enough to me because objects have state and one >>could say that objects represent information.
The fact that objects (specifically object instances) have state and variables have state should be a clue to the observant.
> When discussing data with OO people, I think both the OO people and the data
> centered people focus on the wrong thing. We insist on finding a mapping
> between data and objects.
Frankly, I disagree. I respectfully suggest the data folks do something very different, which is why D&D published the Two Great Blunders.
> I think that's the wrong place to start. I think
> we should start with messages. Every formulation of the OO paradigm starts
> out by saying that objects collaborate with each other by exchanging
> messages. Describing messages in terms of data is a whole lot simpler, and
> less philosophical than describing objects in terms of data. Very very few
> of the OO people insist that there's some metaphysical difference between
> messages and data.
But messages are no different from operations. The idea of messages tends to focus too much on physical implementation or a location-based computational model with the idea that the message moves from one physical location to another. At the logical level of discourse where we actually use operators to identify the operations we use, data has no physical location.
<snip> Received on Mon Nov 03 2008 - 16:49:28 CET