1. A method to be carried out in a computer system that includes a processing unit, a keyboard, a mouse, a display unit and a data storage device, the data storage device having stored thereon a spreadsheet file having at least a sheet with lines and columns, said columns representing fields, said sheet having sheet content with a header portion having at least a designation line with a field designation for each column, and a data portion, wherein each line comprises a record, the method comprising: /a/ identifying a single reference field; /b/ an allocating step in which a field type is allocated to fields other than the reference field, said field type belonging to a set of field types comprising attribute, parent/child, and flow; /c/ defining a link, for each field with an allocated field type, which establishes said link with another linked field, within said sheet or another sheet, wherein: for a field type being attribute, said link is an attribute link and defines properties relative to the reference field or to a parent field; for a field type being parent/child, said link is a parent/child link and defines a membership relationship, wherein a child field belongs a parent field; and for a field type being flow, said link is a flow link and defines a message relative to the reference field; /d/ building a hierarchical model representing the parent/child links, defining at least two hierarchical levels, said model comprising all the fields involved in the parent/child links; and /e/ generating a graphical hierarchical multilevel representation of said sheet content, with at least one graphical view showing one or more hierarchical level and displaying said representation with graphical objects on the display unit.