UN/CEFACT’s Modeling Methodology (UMM) is a UML profile for modeling global B2B choreographies. The basic building blocks of UMM are business transactions, which describe the exchange of a business document and an optional response. In addition to these business document exchanges, UMM business transactions mandate business signals that acknowledge the correctness of business documents. It is expected that a business service interface (BSI) on each business partner’s side reacts on incoming messages and on messages expected but not received. However the internal orchestration of the BSI is open to interpretations. In this paper we demonstrate an unambiguous mapping from global choreographies described by UMM transactions to a BPEL-based orchestration of the business service interface. It becomes obvious that rather simple looking UMM transactions lead to a more complex message exchange mechanism when implemented on top of Web Services.