The BIAN Service Domains define discrete (and comprehensive) non-overlapping business capabilities. It follows that their service operations also define a discrete non-overlapping collection of (high level) business services. This property is increasingly being exploited by using the Service Domains and their service operations to define the service ‘directory’ that can then be implemented using technologies such as an enterprise service bus (ESB). From the ‘application’ side the ESB supports the assembly of business applications from highly re-useable and discrete business services. From the host side host access can be improved using various mitigation approaches such as host session optimization, host access rationalization, data caching and advanced probabilistic data look-up.