userids and subkeys

[Dreweke Alexander]

Hi

I've got a general question about userids and subkeys. I've already read
the manuals but to me it doesn't get clear.

I've got a view email-address which i use in different situations, one
for private, another to universal correspondence, ... . Because of this, 
i created a gpg key for my private address and added subkeys for all
others. So far so good.

-- GPG Manual BEGIN ---
The user IDs associated with your public master key are validated by the
people with whom you communicate, and changing the master key therefore
requires recertification. This may be difficult and time consuming if
you communicate with many people. On the other hand, it is good to
periodically change encryption subkeys.
--- GPG Manual END ---

What exactly is the primary public key is it the DSA key which is used
to sign messages or is it ElGamal key for the encryption? Do i have to
create new just DSA or ElGamal subkeys or both? As far as i understand
the manual it i just advisable to rotate the encryption (ElGamal) key,
which seems reasonable, but would it also make sense to rotate the DSA
key?

Alex