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

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 Received on Tue Jul 24 2007 - 03:08:30 CEST