Generating a contract checker for an SLA language

SLAng is a language for expressing Service LevelAgreements (SLAs) under development as part of the Europeanproject TAPAS. It is defined using a meta-model, an instance ofthe Meta-Object Facility (MOF) model, in which the relationshipbetween the syntax of the language and its domain of applicationis explicitly represented, and the violation semantics ofthe language defined using Object Constraint Language (OCL)constraints. The concrete syntax of the language is the XMLMeta-data Interchange (XMI) mapping of the syntactic part ofthe meta-model. In this paper we describe how the Java MetadataInterface (JMI) mapping can be applied to the meta-modelof the language to generate interfaces and classes to create andquery SLAs and relevant service monitoring data in memory;and how an OCL interpreter can be applied to check violationconstraints over this data, resulting in the implementation of acontract checker that is highly likely to respect the semantics ofthe language

Precise service level agreements

SLAng is an XML language for defining service level agreements, the part of a contract between the client and provider of an Internet service that describes the quality attributes that the service is required to possess. We define the semantics of SLAng precisely by modelling the syntax of the language in UML, then embedding the language model in an environmental model that describes the structure and behaviour of services. The presence of SLAng elements imposes behavioural constraints on service elements, and the precise definition of these constraints using OCL constitutes the semantic description of the language. We use the semantics to define a notion of SLA compatibility, and an extension to UML that enables the modelling of service situations as a precursor to analysis, implementation and provisioning activities