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

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

.

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