Service Problem

Hi All ...

I have a problem .... There is an company which deals in only Sales ans Purchase (Company 1) and there is another company which deals in only service (company 2).... the problem is how can i add expense detail as the service company do not have any inventory item .. and there is no link between these companies ..... company sold goods from company-1 and provide AMC from company-2.... Please help me how can i map the process ..

Thanks & Regards ..