Editing PHIGS (section)

== Technical details ==
The word "hierarchical" in the name refers to a notable feature of PHIGS: unlike most graphics systems, PHIGS included a [[scene graph]] system as a part of the basic standard. Models were built up in a Centralized Structure Store (CSS), a database containing a "world" including both the drawing ''primitives'' and their ''attributes'' (color, line style, etc.). CSSes could be shared among a number of virtual devices, known under PHIGS as ''workstations'', each of which could contain any number of ''views''.

Displaying graphics on the screen in PHIGS was a three-step process; first the model would be built into a CSS, then a workstation would be created and opened, and finally the model would be connected to the workstation. At that point the workstation would immediately render the model, and any future changes made to the model would instantly be reflected in all applicable workstation views.

PHIGS originally lacked the capability to render illuminated scenes, and was superseded by ''PHIGS+''. PHIGS+ works in essentially the same manner, but added methods for lighting and filling surfaces within a 3D scene. PHIGS+ also introduced more advanced graphics primitives, such as [[Non-uniform rational B-spline]] (NURBS) surfaces. An ad hoc ANSI committee was formed around these proposed extensions to PHIGS, changing its name to the more descriptive and (optimistically) extensible name "PHIGS PLUS" -- "PLUS" being a slightly tongue-in-cheek acronym for "Plus Lumière Und Surfaces" (the two major areas of advancement over the base PHIGS standard).