message mapping: table lookup

The requirement:

Source message contains some keys and values, and target message has different keys. Values are simply mapped. no problem. but the mapping between source message keys and target message keys is a bit complicated so it is controlled in a seperate table. End users do maintainance jobs on the mapping table on a daily base.

I checked some threads in this forum and I now understand that this kind of table lookup can be done using the combination of JCo, ABAP programs and ABAP tables, but what is the common way in dealing with such kind of requirement?