[DNA] Re: The difference between identity and identifier (was Re: DNA GoalsIssue List)

[Pekka Nikander <pekka.nikander@nomadiclab.com>]

>> ...  According to my experience, people seem
>> to often have a difficulty in making the subtle but important
>> difference between "identity" and "identifier".
>
> But I think in the case of "link" we have a harder problem as well,
> which is that I sure can't point at the identity of a link.....

> But philisophically, what is a link?
> It isn't an Ethernet switch, or any single physical object.
> And it isn't a set of bits like a storage/disk volume, or a process.
>
> Instead the identity itself feels very amorphous.

For the corner cases, I agree with you.  However, for the vast
majority of practical cases, I would claim that people have no
real difficulty in determining the boundaries of any given
link.  From an IP point of view, and very roughly speaking, a
link seems be consist of the medium that connects those hosts
that are directly reachable, via ARP or ND.  I know, that definition
is bad in many cases, e.g., when proxy ARP/ND is used.  But I
guess you see my point.  :-)

As you mention, the practical difficulty lies in the corner cases,
like partitioning.  We certainly need to think about them, and try
to make sure that our solutions, whatever they be, behave in _some_
sensible way.  And then document the way they behave!

However, for the matter of case, which was DNA goals, I think that
considering links to have some sort of an abstract identity makes
no harm.  We just have to understand that the exact definition of
link identity is not really given a priori but formed by the details
of each solution proposal.

> For these reasons I'm having a hard time pinpointing the identity of 
> the
> link, without talking about the identifiers that have been assigned to 
> it
> by something external to the link object.

When discussing specific technical proposals, I agree that it
is much better to be specific, and think in terms of identifiers.
One may consider identity as an emergent property, "created" by
the details of each solution proposal.

--Pekka Nikander