Reading #11. LADDER, a sketching language for user interface developers. (Hammond)

Comment
Martin Field
Summary

LADDER, is a language to describe how sketched diagrams in a domain are drawn, displayed, and edited. It aims to build a multi-domain system that can be customized for each domain. LADDER is primarily based on  shapes, which means the minimum unit is one shape. A shape includes both geometric information and other useful information, like stroke orders and directions.

The system includes recognition of primitive shapes, recognition of domain shapes, editing recognition, and constraint solver.

Recognition of primitive shapes: To recognize a stroke as an ELLIPSE, LINE, CURVE, ARC, POINT, POLYLINE or some combination using techniques.

Recognition of domain shapes:  It is based on Jess rule, which searches for all possible combinations of shapes that can satisfy it. When a new primitive shape is recognized, it will be added to the system to find whether it can be combined with others. It is bottom-up.

Editing recognition: To recognize the editing gesture, in order to allow users edit shapes.

Constraint solver: To display a shape's ideal strokes by using optimazation functions on  constraints.

Discussion

A great work to design a language for sketch recognition. It is an excellent idea to design a language, rather than design an algorithm. LADDER, is  a more generalized system than others. It can be used in multi-domain sketch recognition.  LADDER is also a framework, so it can combine with others easily.

However, as the paper says, there are still several work to improve LADDER. To some extent, the core of LADDER is the recognition of the primitive shape. It is just bottom-up, can not back-trace. So if there is an error in this stage, then this error will not be removed.  Though LADDER can deal with multiple interpretation from primitive shapes, I think it is better to design a probability based recognition algorithm to solve the problem of multiple interpretation.  The limitation in Section 2.1 is also to be improved.

For complicated shapes, I think it is impossible for LADDER to recognize. LADDER can only recognize what users can exactly describe. Exactly means there is only one shape according to the description.