Hello Meghna,
I don't think you can do what you are describing above. If you have MDM, you are probably using the MDM APIs to save your CRUD requests data into MDM and then you are syndicating it downstream to ECC and other systems. You can't remove MDM from the pictures if your Portal is using the MDM iViews or the Webdynpro Configurable MDM components. Also, you might be using BPM to drive your Portal processes.
MDG is a completely different thing. You can't simply replace MDM with it. MDG is an add-on to ECC. You can have the Co-deployed scenario, where it's installed on the same box as your ECC instance, yes. There is a solution (out of the box) for Material, Customer and Vendor, but it won't be the same as the one you have in Enterprise Portal for the MDM solution. You'll have to configure your new user interface for MDG using Floor plan manager instead. Also, you'll have to use the ECC Business Workflows to drive your approvals.
Hope that clarifies things a little Image may be NSFW.
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Regards,
Boris
