K is a proprietary array processing language developed by Arthur Whitney and commercialized by Kx Systems. Since then, an open-source implementation known as Kona has also been developed. The language serves as the foundation for kdb, an in-memory, column-based database, and other related financial products. The language, originally developed in 1993, is a variant of APL and contains elements of Scheme. Advocates of the language emphasize its speed, facility in handling arrays, and expressive syntax.