Other people have written and explained the usage of Domain Value Maps (DVMs) in Oracle Service Bus already: They can be generated easily within JDeveloper and shared with SCA components of SOA Suite. Previously SOA Composer could be used to modify them.
Here is quick tip: You can now change (or even create!) them within service bus console easily at runtime. So open your service bus console, e.g. from http://localhost:7101/servicebus. Note that the previous /sbconsole is now /servicebus and comes with a fresh look. The old URL is still working but deprecated and should not be used anymore.
Btw there were other XQuery based approaches that also allowed DVM to be used and changed at runtime, but the built-in DVMs are easiest and most convenient.