DB Compare is a tool that can compare two different schemas. These can be in the same database, or different databases, as long as you can log on to each of them.
It builds on Reverse DDL Engineer's ability to parse metadata and turn it into CREATE, ALTER and GRANT statements by prompting the user for two logons. As soon as the second user is logged on, it goes to work, building a tree view of all the various types of objects and highlighting those that are different between the two.
The initial display makes clearly identifies items found in the second schema but not the first. These are labelled "added." Items in the first but not the second are considered "removed."
The third category, as you might expect, is "changed"--objects present in both schemas with differences in their DDL. When you highlight one of these, the DDL for each is displayed side by side.
Besides detailing the differences, a ready-made script gives you the option of making the second schema look like the first through a series of DROP and CREATE statements. Just run the entire script or the parts that you deem appropriate. Objects compared include indexes, constraints, sequences, all types of PL/SQL and anything else belonging to the schema.
See this example to understand how DB Compare works.