Reading #11: LADDER, a sketching language for user interface developers (2007)

by Tracy Hammond and Randall Davis (paper)

Comments: Jonathan

LADDER is a language to "describe how sketched diagrams in a domain are drawn, displayed, and edited." It is intended to help interface developers create sketch-based interfaces. LADDER is used to create shape descriptions. Shapes consist of components (such as lines), constraints (such as intersections), aliases, editing, and display properties. LADDER descriptions allow domain-specific definitions that can be used with domain-independent recognizers.

The paper gives many examples of shapes that can be modeled using LADDER. Such shapes include arrows and UML diagrams.

There are many predefined shapes (such as point, line, curve, ellipse), constraints (such as perpendicular, collinear, tangent, larger, acute), orientation-dependent constraints (such as horizontal, negative slope, above, centered below), editing methods (such as click, draw, encircle), and display methods (such as original strokes, ideal strokes, circle, rectangle, text, image).

Some shapes can be made up of certain numbers of segments, while some shapes can be made up of infinite segments.

When recognition occurs, primitive shapes are recognized first. Shapes are generated that contain the original strokes and their interpretations. Some shapes contain sub-shapes. Once primitive shapes are recognized, domain-specific shapes, using the domain descriptions, are recognized.

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LADDER is a nice tool for interface developers. I like that it allows complex shapes to be completely described using a programming language. However, I do see certain drawbacks, namely that each shape must be explicitly defined in LADDER. The paper mentions the capability to generate descriptions based on drawn examples, and I think this would be a great idea. It would be very tedious to define explicit shapes for large domains (COA...). I don't know if it has been implemented yet.