In most common data compare scenarios, the default mapping mechanism employed by Data Compare for Oracle, pairs the tables and views based on the name. However, there are often scenarios in which tables and views in both databases being compared may have slightly different names. Of course, as explained here, you can manually pair any two tables or views regardless of their names but that requires a lot of effort and makes sense when the names are completely different. In cases when, let's say, you may have table names in database1 prefixed with prefix1_ whereas the equivalent tables on database2 prefixed with prefix2_, you can utilize the mapping rules to make your job easier. Mapping rules allow you to automate the pairing of those tables by creating simple rules.
The Mapping Rules can be accessed from the ribbon or from the action links on the right panel of the comparison tab. There are two basic rules you can set, "Ignore prefix" and "Ignore postfix". For example if you wish to map prefix1_employees from database1 to employees table from database2 then you just enter "prefix1_" in the "Source table prefix" textbox - that will cause the "prefix1_" part of the table name to be ignored in database1 and map the tables only based on the part of the name that comes after that part. Similarly, you can ignore a prefix on the other database, so you could easily have prefix1_employees table mapped to prefix2_employees table. You can do the same thing with "postfixes", so you could map employee_postfix1 to employee_postfix2. This is a small feature but comes in very handy in certain scenarios.
Download Data Compare for Oracle and try today - it comes with a 3 week free trial.