Hi,
I went through the below link
Design Time: How to Compose Multiple OData Services using SAP Gateway
I created two services.
My second service is in the current (same) system.
I created the external association and also generated the run-time objects.
However, I was not able to register using service maintenance feature.
1) How to register using service maintenance? Is it mandatory?
Because when I click on service maintenance, everything Register and Maintain buttons are graded out.
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When I clicked Call Browser button after activating the main service, I was able to see the dependent service details also in the XML (browser).
2) Can I use $expand in the url to expand the second (dependent) service?
As I am using multiple service and I don't want to use a single service.
I want to link this way instead of creating multiple entity sets in the same service.
Is it possible?
Any suggestions would be helpful 
Regards,
Gopa