  Because spreadsheets have a large and growing importance in real-world work,
their contents need to be controlled and validated. Generally spreadsheets have
been difficult to verify, since data and executable information are stored
together. Spreadsheet applications with multiple authors are especially
difficult to verify, since controls over access are difficult to enforce.
Facing similar problems, traditional software engineering has developed
numerous tools and methodologies to control, verify and audit large
applications with multiple developers. We present some tools we have developed
to enable 1) the audit of selected, filtered, or all changes in a spreadsheet,
that is, when a cell was changed, its original and new contents and who made
the change, and 2) control of access to the spreadsheet file(s) so that
auditing is trustworthy. Our tools apply to OpenOffice.org calc spreadsheets,
which can generally be exchanged with Microsoft Excel.
