In order to successfully integrate OLTP systems, two main issues need to be addressed. First, every application, or group of applications, that will be considered as an independent processing entity with well-defined boundaries should have a rich meta-information repository. This repository will unambiguously define all the relevant data within the scope of the business processes supported by this system. For instance, I was recently part of an effort where the domain model had three main parts: business class model, business use case realizations, and system use case model. No data element would be added to the domain model unless it was initially called out in the business and system use cases.