Re: What is that "more" that makes E-R model truly independent ?

beginner16 wrote:

> hello
>
> 1)
>
> Before I ask the question I must point out that I understand the
> difference between logical and conceptual level. Thus, conceptual
> model represents DB design independently of the underlying logical and
> physical structure. I also realise that hierarchical and relational
> models are at logical level!
>
> I just started learning a little about E-R model. I realize the E-R
> model was created so that we can represent DB at the conceptual level,
> and as such DB is presented independently of the underlying logical
> DB design.
>
> Say we are trying to create DB for particular organization. At
> conceptual level E-R model for this DB would be the same no matter if
> logical implementation of this DB will be hierarchical or relational
> ( I realize that this is probably not always true )
>
> We could implement same graphical symbols ( let us called this set of
> symbols with "S" ) to represent objects, relationships etc in both
> relational and hierarchical models, but when trying to represent DB at
> conceptual level using these symbols, ( I assume ) the two diagrams
> ( hierarchical and relational ) would still be very different, even if
> both relational and hierarchical models would use same graphic
> symbols?!
>
> But as I stated before, E-R model diagram would be the same no matter
> if logical DB implementation is hierarchical or relational. For that
> reason I assume that ER modeling is more than just using symbols for
> entity, attributes, relationships ( since relational and hierarchical
> models use same "fictional" graphical symbols and still their diagram
> representations of DB at conceptual level differs ). But what is that
> "more" that makes E-R model truly independent of logical DB
> implementation ?
>
> 2)
> Does relational model also have its own graphical symbols defined
> ( for graphical representation ) or do we always need "outside"
> diagrams ( E-R model, Bachman's model etc ) in order represent it
> graphically?
>
> thank you
>
> cheers

Pretty pictures are intellectually limiting crutches. Received on Tue Jul 24 2007 - 04:22:14 CEST