Service-level agreements (SLA) definition and monitoring are open issues within the IT Service Management (ITSM) domain. Our main goals are to propose a model-based approach to IT services SLA specification and compliance verification. The specification will be accomplished by proposing a SLA language - a domain specific language for defining quality attributes as non functional requirements (NFRs) in the context of ITSM. This will allow that SLA monitoring and compliance validation at a level of abstraction that is understood by the stakeholders involved in the service specification.