Re: I still don't understand whether the term data model...

<kaja_love160_at_yahoo.com> wrote in message news:1184854260.316035.91780_at_x35g2000prf.googlegroups.com...
> hello
>
> 1)
> I still don't understand whether term data model (or data model
> instance) refers to mechanism ( implemented as software ) that defines
> what kind of structures ( tables, relationships etc ) system
> administrator can create using SQL statements, or does the term refer
> to actual structures the system administrator created using SQL
> statements?
>
> For example, say I create ( in relational database ) a new database
> consisting of one ( or more) table. Now does term logical data model
> refer to this very table I created, or does the term relate to
> mechanism that defines what kind of structures ( in relational DB ,
> for example, this mechanism allows table structures ) we can create
> and what kind of connections we can establish between these tables?
>
>
> 2)
> And how does a scheme fit into all of this?
>
> thank you
>

Your confusion is justified because it seems that "data model" is commonly used with at least two meanings, which you have correctly identified.

From "The Relational Database Dictionary":

<quote>

data model

1. An abstract, self-contained, logical definition of the data structures, data operators, and so forth, that together make up the abstract machine with which users interact.
2. A model of the persistent data of some particular enterprise (i.e., a logical database design).

</quote>

"The Relational Model" is an example of the first meaning. "A logical model" is the second.

-- 
David Portas