To refresh Materialized views, you can use any of the following two APIs – DBMS_MVIEW and DBMS_SNAPSHOT
There is no difference between using DBMS_MVIEW and DBMS_SNAPSHOT. Both packages are identical in their behavior, the supported method from 8i onward is to use DBMS_SNAPSHOT
However DBMS_REFRESH is used for Refresh Groups and is different to the above two. This enables to create Groups that can be refreshed together to transactionally consistent point in time.
Oracle Enablement 