A translation layer is used when two sub-models interact with each other. This translation layer is used when you integrate models with an external system. This works fine when you have one sub-model that uses this external system. The Open Host Service is required when more than one sub-model interacts with external systems. Then, the Open Host Service removes any extra or duplicated code, because then you need to write a translation layer for each sub-model's external system.

An Open Host Service provides the services of an external system using a wrapper for all sub-models.