You have some choices here:
- add a couple of extended attributes to columns in your PDM to hold the required data - you can easily import this from Excel if you want to
- this does't give you traceability from object-to-object, just text
- reverse-engineer your source databases, and map them to your target PDM via the mapping editor or a data movement model
- this gives you better traceability
- if you can't reverse-engineer your databases, you could create simple PDMs using Excel import - if you can reverse-engineer them later, you can get the new model to 'take over' the mapping by merging carefully.
- create a data movement model, add your sources as flat files with columns, then link them to the columns in the target PDM
- tricky to get right, but you don't need a PDM