International standards and references about ITSM, like ISO 20.000 and ITIL, deal with the management of service quality, define SLAs (e.g. availability, response time, etc.), and how to manage them from a process perspective. These definitions can be applied both to a service provided by a single provider under a single Service Level Agreement and, in more complex scenarios, to a service made up by the combination of several services provided through multiple contracts. The latter scenario brings to light issues and aspects relevant to the business and to the IT staff. The paper proposes an approach to model SLAs in complex service systems by means of check points. The model supports Service Level Managers in dominate SLAs both from technical and contractual perspective and facilitates communication with business. A case study is used to motivate and exemplify the model.