Abstract: An apparatus for storing data for use in displaying diagrams comprises a computer and a file server. Each diagram includes boxes and flow lines connecting the boxes. The software includes a database and a main program which is responsible for storing and retrieving diagram data as well as performing predetermined operations on the data. In the database, data describing a box is stored as an instance of a first software object class, data describing a flow line is stored as an instance of a second software object class, general data relating to a diagram is stored as an instance of a third software object class, and data describing the location of each entity (box or flow line) on a diagram is stored as an instance of a fourth software object class.