Description Logic

I've been having some issues with description logic recently. I can't tell the difference between value restriction (∀R.C) and role restriction (R|_C). These have the semantics of:

 ∀R.C      {x ∈ ∆^I | ∀y.(x,y) ∈ R^I → y ∈ C^I}
R|_C      {(x,y) ∈ ∆^I × ∆^I | (x,y) ∈ R^I ∧ y ∈ C^I}

Value restriction (∀R.C) uses an "implies" operator (→) to say that any use of the role will refer to an instance of the class C. Implication means that there can be values for y which are not part of the role description, and are still instances of C. However, since we also have a universal qualifier for y when used in the role, then we have no need to consider elements of C which are not used in the role.

Role restriction says that for any use of the role, then the value in that role (y here) will also be an element of C.

Given that value restriction has the universal quantifier on y, I don't see the difference between the implication here, and the conjunction used in role restriction.

So to me, value restriction defines a class where all uses of a role refer to elements of a specified class (C), and role restriction refers to a role that can only refer to elements of a class. They means slightly different things, but then I don't understand how (∀(R|_C).A) is any different to (∀(R).(A⊓C))

Maybe I'm reading it wrong.

Anyway, I think it's because I don't understanding this difference that I can't get the following property:

(∀(R|_C).A) ⊓ (∀(R|_D).A)     ≡    ∀(R|_{(C ⊔ D)}).A

My reading of it says that the right hand side should include an intersection of (C ⊓ D) and not the union (C ⊔ D).

I know I'm wrong here, but I just don't see it. Unfortunately, I don't know where to ask either. Can anyone help?