Testing carried out to show that a product meets the requirements of a relevant standard. Typically conformance testing is carried out for compilers (thus compiler validation), and for products that implement interface specifications such as for OSI or EDI. The testing will usually be carried out by a third-party organization approved by the appropriate national body, will use an approved conformance test suite and conformance test procedure, and will result in the issue of a conformance certificate for the product. Usually a certificate will be of limited duration, typically one year, when retesting will be required. If a product is altered in any way retesting will also be required.