In the software development process, a reference implementation (or, less frequently, sample implementation or model implementation) is the standard from which all other implementations, with their attendant customizations, are measured, and to which all improvements are added. An improving reference implementation in turn reflects its unchanging specification, or else an attempt at an implementation may prove that the specification is impractical and needs improvement itself.[clarification needed] Testing the implementation-specification relationship further enhances the production's inter-process efficiencies:
A reference implementation is, in general, an implementation of a specification to be used as a definitive interpretation for that specification. During the development of the ... conformance test suite, at least one relatively trusted implementation of each interface is necessary to (1) discover errors or ambiguities in the specification, and (2) validate the correct functioning of the test suite.
Characteristics of a Reference Implementation: (1) Developed concurrently with spec and test suite; (2) Verifies that specification is implementable; (3) Enables the test suite to be tested; (4) Serves as Gold Standard against which other implementations can be measured; (5) Helps to clarify intent of specification where conformance tests are inadequate
A reference implementation may or may not be production quality. For example, the Fraunhofer reference implementation of the MP3 standard usually does not compare favorably to other common implementations, such as LAME, in listening tests that determine sound quality.
Reference implementations may also be prohibited by licensing for commercial use. For example, The Sun Microsystems Java EE RI application server is referenced by a great deal of Java EE training literature. However, it cannot be licensed for production use.