1. A computer apparatus for generating and displaying a pictorial representation of a Boolean expression, the apparatus comprising: a processor; at least one processing device for executing stored program components; an input component for inputting the Boolean expression to be pictorially represented into a form of a binary tree in which a leaf node represents an operand in the Boolean expression and a node other than the leaf node represents an operator in the Boolean expression; a transforming component for transforming the binary tree into a two-dimensional nested representation composed of a plurality of regions; and a drawing component for drawing a pictorial representation for visualization on the basis of the nested representation; a storage memory for storing the binary tree input by the input component, the nested representation created by the transforming component, and the pictorial representation drawn by the drawing component; and a display for visually displaying the pictorial representation, wherein the nested representation is composed of at least one nested object containing a plurality of nodes and wherein the transforming component transforms a leaf node of the binary tree into a nested object having a label of the leaf node and a flag, and highlights an operand corresponding to the leaf node when the flag is set to a first value and highlights a region enclosing the operand when the flag is set to a second value.