Sketch Recognition Algorithm for Spider diagrams Mithileysh Sathiyanarayanan University of Brighton, UK M.Sathiyanarayanan@brighton.ac.uk Abstract. Spider diagrams are a combination of Euler diagrams and graphs. These two are a popular and frequently used visualization tech- nique in many application areas. Euler diagrams and graphs serve as an information tool. There are intelligent tools which allow sketching of Eu- ler diagrams and graphs in combination. Existing tool for creating Euler diagrams and graphs in combination, called as spider diagrams by us- ing mouse and keyboard interaction are also available. In this research, we propose an algorithm which will sketch spider diagrams considering wellformedness properties and syntax matching, so that any semantic differences introduced when converting sketch to formal can be auto- matically identified and rectified, as done for Euler diagrams. 1 Introduction Euler diagrams [1] are collections of closed curves used to visualize relation- ships between sets. They represent inclusion, exclusion and intersection of sets. Graphs [2] are a combination of vertices and edges used to visualise relationships between data items. Euler diagrams and graphs are very popular and widely used information tool for visualizing data. Both in combination can be used in wide- ranging practical use. Spider diagram [3] is a diagram which has curves with labels, some shaded zones, vertices and edges. In previous works [3], vertices with edges in different zones were called as spiders. So, considering spider dia- grams which uses both Euler diagrams and graphs, there is a need to provide convenient ways of creating these diagrams in electronic form. The created dia- grams using the software (using mouse and keyboard interaction) will have some understanding of the diagram semantics. In a sketching context [4], SketchSet is used for creating Euler diagrams us- ing pen and mouse along with a interactive device (like computers or tablets) where users can produce, evaluate, modify, refine and replace diagram compo- nents rapidly. If a computer understands the sketch it can be more easily edited, animated and translated from one format to another. Pen-input computers mean the drawing can now be done directly on the interactive screen. Automatic and reliable recognition of hand-drawn diagrams is now becoming possible as demon- strated in [5]. The tool, called SpiderSketch [6] is developed to allow users to sketch spider diagrams which recognises each pen stroke. Previous work on sketch recognition