Business scenarios such as Business Value Networks and Extended Enterprises pose new challenges for service choreographies across heterogeneous Virtual Organizations. In such scenarios, services compose together hierarchically in a producer-consumer manner to form service supply-chains of added value. Service Level Agreements (SLAs) are defined at various levels in this hierarchy to ensure the expected quality of service for different stakeholders. Automation of service composition directly implies the aggregation of their corresponding SLAs. But so far, the aggregation of SLAs has been treated only as a single layer process which is insufficient to complement the hierarchical aggregation of services. In this paper we elaborate on the requirement of a hierarchical aggregation of SLAs corresponding to service choreographies in Business Value Networks. During the hierarchical aggregation of SLAs, certain SLA information pertaining to different stakeholders is meant to be restricted and can be only partially revealed to a subset of their business partners. We introduce the concept of SLA-Views to protect such privacy concerns. We, then formalize the notion of SLA Choreography and define an aggregation model based on SLA-Views to enable the automation of hierarchical aggregation of Service Level Agreements. The aggregation model has been designed to comply with the WS-Agreement standard.