SLA★: An abstract syntax for Service Level Agreements

This paper describes SLA*, a domain-independent syntax for machine-readable Service Level Agreements (SLAs) and SLA templates. Historically, SLA* was developed as a generalisation and refinement of the web-service specific XML standards: WS-Agreement, WSLA, and WSDL. Instead of web-services, however, SLA* deals with services in general, and instead of XML, it is language independent. SLA* provides a specification of SLA(T) content at a fine-grained level of detail, which is both richly expressive and inherently extensible: supporting controlled customisation to arbitrary domain-specific requirements. The model was developed as part of the FP7 ICT Integrated Project SLA@SOI, and has been applied to a range of industrial use-cases, including; ERP hosting, Enterprise IT, live-media streaming and health-care provision. At the time of writing, the abstract syntax has been realised in concrete form as a Java API, XML-Schema, and BNF Grammar.