I. Introduction
The ICT service-provisioning infrastructure and related digital ecosystems are increasingly complex and evolving systems where services delivered involve multiple business entities (stakeholders) sharing the responsibility of providing robust, dependable and predictably high performance services. A textbook example for such a complex ecosystem is that of anticipated 5G verticals, which hold the business potential of being true value-added services [1]. Such verticals inherently require strict end-to-end Quality of Service (QoS) guarantees and the collaboration of mobile and fixed network operators, cloud infrastructure owners and Over-The-Top (OTT) providers, comprising a multi-actor value chain. This inevitably calls for multi-operator business, service and resource coordination, which is in the focus of the in-progress H2020 5G-PPP 5G Exchange project (5GEx) [2]. While emerging concepts such as the softwarization of the network control plane (Software Defined Networking, SDN) and the virtualization of resources and network functions (Network Function Virtualization, NFV) can serve as powerful technological enablers, the business framework including inter-stakeholder contracts, resource trading and coordination models require its own (but integrated) mechanisms.