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Utility computing (UC) is concerned with the provisioning of computational resources (compute-power, storage, network bandwidth), on a per-need basis, to corporate businesses. Service-level agreements (SLAs) - contracts between a provider and a customer - are a sine qua non in the deployment of UC. A crucial stage in the life-cycle of contracts (such as SLAs) is their automated performance monitoring while active; a significant aspect of which concerns the tracking of contract state. In this work, we define an ontology to capture aspects of SLAs that are pertinent to the tracking of state for performance monitoring, and generalise these aspects so that the ontology may be applicable to other contract domains. The ontology is formalised as an XML-based language, called CTXML (contract tracking XML). The semantics for CTXML are presented in terms of a computational model based on the event calculus.