Key Conversion using Java mapping

Hello everybody,

Maybe someone of you had the same situation so I'm looking for your advice for the best solution.

What I have:

2 different systems should exchange their data via XI.

Every record in one system has a corresponding record in another. Surely they have different primary keys in their own native systems.

What I need:

I need that by changing the record in one system corresponding record in another system would reflect all those changes, so change information would replicate from one system to another.

What I suppose to do:

1. Build a conversion table that would store primary keys from both systems.

2. Place that table inside XI database.

3. Write Java mapping that would take responsibility to make an id's conversion (connect to that conversion table, select needed key etc.).

What do you think of that? Is there any other way to make such kind of conversion? Is that more natural to use any ABAP mapping functions? Please take in account I cannot change records in the systems, it means I cannot add any extra fields to them and conversion should be done in XI.

Thank you,

Looking for your suggestions,

Igor