United States Patent  [in Patent Number: 5,055,998
Wright et al.  Date of Patent: Oct. 8, 1991
changed among spreadsheet programs. The intermediate spreadsheet structure represents a spreadsheet as a set of nested segments. Each non-empty cell of the spreadsheet is represented by a cell segment. All of the cells belonging to a first-dimensional element of the spreadsheet such as a row are contained in a vector segment representing the row; All of the vector segments representing elements of a second-dimensional element such as a matrix are contained in a vector segment representing the second-dimensional element. The same type of nesting is used with all higher-dimensional elements. Each segment further contains descriptors which define certain aspects of the segment's content. The cell segments may further contain an expression control and descriptors belonging to the expression control which define an expression. The descriptors belonging to the expression control define the expression's operands and an operator. Operands may be constants, references to other cells of the spreadsheet, or another expression. Nesting of expressions is permitted to any practical depth. Other aspects of the spreadsheet specified by descriptors include the manner in which the spreadsheet and its contents are to be formatted when it is displayed, access control for portions of the spreadsheet, the data types of values, and rules for the order in which have the values of the cells in the spreadsheet are computed.