Provisioning is based on OVM templates (almost similar to VMware template), and oracle provides preconfigured templates for their db/middleware etc.
Here are 2 papers from oracle..
“Oracle Optimized Solution for Enterprise Cloud Infrastructure is a
complete, integrated solution which can dramatically reduce the time required
to architect, deploy, and manage Infrastructure-as-a-Service clouds, and
ultimately lower TCO and improve productivity for enterprises and cloud
Added Oracle Exadata details