Into the CMDB, service modelling is component centric today. For example, if we want to connect two services (a. Application; b. Firewall) and the application uses only part of the service (Firewall Cluster b1), you need to connect it directly to the component (a to b1). This is not service centric.
A service centric approach would let you connect service to service and define what components are being allocated to support these connection.
If you suffer with this problem, please let's bring this functionality to the CMDB/SDM.