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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 signal reflection resulting in attenuation and noise. See also impedance matching.

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. Christopher J. Date would argue that a truly relational DBMS would pose no such problem, as domains and classeses are essentially one and the same thing. Another significant impedance mismatch in programming occurs between the domain objects and the user interface.