An idiomatic illustrator is a special-purpose graphics tool that enables the construction of a particular class of real-world illustrations. The illustrators for Star are curve graph, bar chart, pie chart, diagram, map, plan, and perspective. While each illustrator is conceived of as a self-contained illustration machine, they will all operate within the general graphics environment. In particular, all illustrators are composed of transfer symbols, making them graphic constructions.

In terms of graphic language, an 'idiom' is an expression whose form structure and meaning are peculiar to a specific class of images. It is a constrained form/space environment which operates by certain conventional rules to produce certain visually communicative effects. Thus in Star the bar chart illustrator is a machine for constructing illustrations in the graphic idiom of bar charts.

The purpose of the idiomatic illustrator is to enable Star users without professional graphic skills to create quality illustrations. Many of the graphical operations in conventional illustration are rational, measurable, and repetitive, and can be successfully represented in a machine system which does most of the actual graphic construction. Idiomatic illustrators are designed to provide the user with more specific drawing supports than are provided by the general graphics tools. The office graphics user does not need the whole world of graphic language at his command to create, say, a bar chart; all he needs are a scale and some bars and labels. On the other hand, if he would rather make a pie chart he doesn't need bars and scales; he needs only a circle and some dividing lines and labels. Thus in Star, the bar chart illustrator only draws bars, and the pie chart illustrator only draws pies. Too constrained? Not for the unskilled user who simply wants a bar chart now without first having to master the professional illustrator's bag of tricks, both technical and esthetic. For the unskilled user, constraint means support. The user enters the graphics world at the application level, where he can represent his ideas and information using recognizable illustration elements (bars, scales, pie slices, etc.) rather than the more general form elements (lines, shapes, etc.) which are the conventional resources of the skilled graphics specialist.

While most graphic design decisions are reserved for the user, the actual drawing of the image is intended to be as automated as possible. This (1) enables the user to produce illustrations which might otherwise exceed his manual skills, (2) relieves the user from the burden of 'mindless' repetitive graphic operations, (3) maximizes the technical quality and consistency of the resulting illustrations, and (4) minimizes the time it takes to draw them.

The three basic levels of design and execution in the idiomatic illustration process are called spatial grammar, form vocabulary, and visual editing.

Spatial grammar includes the global features which control the overall spatial structure, size, and scaling of the illustration. Included are the specific graphic objects which represent these global characteristics, such as grid scales, guidelines, perspective planes, etc. The purpose of spatial grammar is to provide a compositional framework for the construction, placement, and in some cases the measurement of form elements in the illustration.

Form vocabulary includes the intermediate-level graphic objects which represent the subject matter elements of the illustration, such as bars, curves, pie slices, blocks, symbols, location points, routes, areas, shapes, volumes, etc. Their purpose is to provide the user with an appropriate range of prefabricated form elements and property options to satisfy both the technical and the esthetic requirements of the idiomatic illustration. These elements are transfer symbols. Spatial placement of form elements is automated wherever appropriate, and is otherwise manual.

Visual editing includes special modifications, additions, and/or deletions of form details on the lowest level of form selection. General graphics tools are used on this level to enable a higher degree of individualization in the illustration: to improve its appearance or esthetic impact, to enable stylistic details, to visually relate or differentiate parts, to emphasize or subordinate particular elements, to make technical corrections, to add supplementary notes or labels, and to generally polish the illustration to make it a more articulate visual statement.

These three levels of graphic design/execution apply in a specific sense to the particular communicative aims of each illustration idiom. Briefly, the communicative aims of the idiomatic illustrators are as follows: