diff in version liquibase-2.0-rc7 requires referenceUrl parameter

When trying to run the diff command on two databases I got the error:
Liquibase Update Failed: referenceUrl parameter missing.  For more information, use the --logLevel flag)

The command I run looks like this:

liquibase --driver=oracle.jdbc.driver.OracleDriver

When running it in version 1.9.5 it works fine.

  1. What should I specify with parameter referenceUrl?
  2. If I must use it, why is it necessary to use the referenceUrl parameter when I want to compare two databases?

In 2.0, the baseUrl, baseUsername, etc parameters used in performing database diffs have changed to referenceUrl, referenceUsername, etc. They should point to your database of reference, not the one you are wanting to update. 

The name change was to try to remove confusion.