Reading 21: LADDER, a sketching language for user interface developers

Citation

Hammond, Tracy, and Randall Davis. "LADDER, a sketching language for user interface developers." Computers & Graphics 29.4 (2005): 518-532.

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Summary

This paper presents LADDER which is a language to describe how sketches are drawn, displayed or edited in a domain. These descriptions are then transformed into actual recognizers which can recognize and show the described behaviors of displaying and editing the recognized sketch. Such system will let any scientist to create a sketch recognition system tuned for a particular domain by specifying all the shapes that need to be recognized for that particular domain.

The five main things that define a shape in LADDER are:

1) Components: The components (mainly primitives) consisting of the new shape.

2) Constraints: Constraints on how the components are organized in the sketch.

3) Aliases: Giving names to components that can be reused describing certain properties.

4) Editing: Set of triggers and actions which describe any editing behavior on the sketch. Such as double clicking the shape should case it to get selected.

5) Display: How the shape should be displayed, should the components be used as original or beautified or should some color be applied to the stroke. 

Discussion

LADDER is also hierarchical so new shapes can be described by using existing defined shapes. It also supports abstract shapes so that shapes belonging to a particular category inherit certain properties from a common parent class. 

An example description for an arrow shape is shown below: