DKIM vs Domain Keys

I've configured DKIM (milter-dkim) on my mail server. Incoming e-mail sent from my domain now containts the following header:

X-DKIM: Sendmail DKIM Filter v2.8.3 MYDOMAIN.com o7FLH1Wa032083
DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=mydomain.com; s=mail;
 t=1281907022; bh=frcCV1k9oG9oKj3dpUqdJg1PxRT2RSN/XKdLCPjaYaY=;
 h=Message-ID:Date:Subject:From:To:MIME-Version:Content-Type:
  Content-Transfer-Encoding;
 b=qetPkilXBdjnuqiKIyvAwsvTvJfAnq5urdgp/i7p/uLJ8DB+svy9A8C6CPmcfELsJ
  hDid5k2AN5JD+wM2INmUIgjeAa/IwpGTbuMloj0Wioh4njqIfbATJqOhuqxTjic

1.) So I guess that confirms that I have DKIM setup correctly, right?

But when I look at a message coming in from Google, I see:

DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
        d=gmail.com; s=gamma;
   ...snip...
DomainKey-Signature: a=rsa-sha1; c=nofws;
        d=gmail.com; s=gamma;
   ...snip...

2.) What is the relationship of DomainKey-Signature vs DKIM-Signature?