WS-Agreement is a language and protocol designed for creating service-level agreements (SLAs) based on initial offers, and for monitoring those offers at runtime. The definition of WS-Agreement protocol is very general and does not contemplate the possibility of changing an agreement at runtime. This paper presents extensions of the WS-Agreement specification to support the dynamic nature of SLAs by allowing the possibility of SLA renegotiation at runtime. The extended WS-Agreement specification has been implemented and tested. Within this implementation, the concept of renegotiation is demonstrated through the ability to create more than one SLA at runtime. An evaluation is conducted to examine the profits a service provider may gain through renegotiation, as well the savings resulting from rescuing the SLA from violations as a consequence of avoiding paying penalties. The results show that making the SLA terms adaptable and changeable is a viable mechanism that provides flexibility to the service provider and service consumer.
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