Acronym for Programmer's Hierarchical Interactive Graphics System, the ISO/IEC 9592 standard. Many of the concepts of GKS are present in PHIGS (workstations, input model, attribute handling, etc.). However, PHIGS is primarily a three-dimensional standard aimed at providing high-quality views of graphics objects that are hierarchical and made up of many subparts (e.g. a vehicle). Lighting and rendering extensions together with a number of high-level primitives are included in Part 4 of the standard, called PHIGS PLUS. PHIGS was superseded by OpenGL in the 1990s and is no longer used.