LADDER: A language to describe drawing,,display,andediting in sketch recognition
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We have created LADDER, the first language to describe how sketched diagrams in a domain are drawn, displayed, and edited. The difficulty in creating such a language is choosing a set of predefined entities that is broad enough to support a wide range of domains, while remaining narrow enough to be comprehensible. The language consists of predefined shapes, constraints, editing behaviors, and display methods, as well as a syntax for specifying a domain description sketch grammar and extending the language, ensuring that shapes and shape groups from many domains can be described. The language allows shapes to be built hierarchically (e.g., an arrow is built out of three lines), and includes the concept of "abstract shapes", analogous to abstract classes in an object oriented language. Shape groups describe how multiple domain shapes interact and can provide the sketch recognition system with information to be used in top-down recognition. Shape groups can also be used to describe "chain-reaction" editing commands that effect multiple shapes at once. To test that recognition is feasible using this language, we have built a simple domain-independent sketch recognition system that parses the domain descriptions and generates the code necessary to recognize the shapes.
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