CHAPTER 9: Building the Agile Database 171 Cohesion and Coupling Two other important Object-Oriented concepts affecting database issues are Cohesion and Coupling. We've talked about Coupling before; the goal is to keep applications and databases "loosely coupled" so that changes to the database schema have a minimum impact on applications, and databases can support multiple applications and multiple uses of data. Cohesion is the other side of the coin: all data needed to support the properties of an application object should be available in one place. On the surface, these two goals appear to be mutually exclusive. As we've seen, we help achieve "loose coupling" by keeping the base schema of the database more-or-less normalized (for OLTP databases) and application-independent. But this scatters data needed by application objects throughout the database, making it harder to achieve cohesion. How do we reconcile these two goals? You know the answer: we achieve the cohesion we need by