Impedance mismatch

Impedance mismatch is a problem in electrical engineering that occurs when two transmission lines or circuits with different impedances are connected. This can cause various losses and noise.

In programming terminology it refers to the attempt to connect two systems that have very different conceptual bases, most commonly when trying to use a SQL database from an object oriented program. A really relational DBMS would pose no such problem, as domains and classes are essentially one and the same thing.