Diff. between Business service & Business system.

Hi All,

Can anybody tell me what is the actual difference between Buss. service & system ? and in which case I should use either ? How can I differenciate this two ?

Eg. 1. I am using Buss. system BS1 , than what/where this BS1 should be ? and 2. if am using Buss. service BS2 , than what/where this BS2 should be ?

Thanks.

Ramiz.