I have seen two ways to deploy DMZ's. One has an interface off the ASA become a DMZ and then you configure all the associated rules, NAT etc for traffic flow, inside to DMZ and DMZ to inside.
I have also see ASA's deployed with a simple Inside and Outside port arrangement with a DMZ layer present just inside the ASA inside interface and then another firewall (ASA or FWSM) upstream from that. Is one better than the other, or, more recommendable than the other?
The DMZ services in this case can be considered to be, email server, web portal, in-line IDS.