A simple diagram editor is used to design a diagram on a sheet. A sheet is a collection of links

and boxes. A box has a size, position on the page, color, and may optionally contain some text.

A link is a sequence of line segments that connects two boxes. Each line segment is either

horizontal or vertical, and connects two points. A point may be shared by a vertical and

horizontal segment in the same link. A buffer is a collection of links and boxes that have been

cut or copied from the sheet. Note that a link or a box belongs to one buffer or to one sheet.

The user can add, move, or delete links or boxes. Elements can be cut, copied, or pasted to the

buffer, and the sheet can be read from a file, written to a file, or printed.