Do you want to ensure the correctness of your spreadsheets?
Do you need to review spreadsheets made by others?
If so, Spreadsheet Verificator is your best friend!
- Spreadsheet Verificator verifies all the cell values and formulas
of your spreadsheet by types.
- It either proves that the spreadsheet is exempt of a class of typing errors,
or identifies the cell formulas that contain typing mismatches,
which are clues to spreadsheet defects.
- As a result, verifying and validating spreadsheets by Spreadsheet Verificator
will improve their quality and
prevent you from making business decisions with incorrect spreadsheets.
Elements in the Task Pane
- 1 button
- 1 result area
- 1 link to the support page
Must-do Before Running the Tool
- unprotect manually the worksheets protected with password, if there is any
- Comparison.xlsx: an artificial simple example to show a comparison of a string and a double does not lead to an obvious error (eg, #VALUE) in Excel, though such a comparison does not make any sense in reality.
Spreadsheet Verificator will detects a typing error: "AVERAGE(Double, Double, Double, Double, Empty)", from where we could observe that the last argument of the formula does not point to the correct cell.
A "Currency-String" typing error will be raised by the verificator;
it reveals that the value of a cell is incorrectly entered.
A "Double/String" typing error raised by the verificator will
reveal the incomplete part of the spreadsheet.
Brief Description of our Verification
Why Should Spreadsheets Be Verified by Tools?
- Spreadsheets are error-prone,
because errors in spreadsheets are not blocking
- Spreadsheets are carriers of important business information, data and logic
Spreadsheets can be big and complex, or made by others;
they are hard to review thoroughly.
Verification by Types
Type checking is a classic, popular, and effective method to verify computer programs.
It is even systematically applied to programs written in certain languages
such as OCaml, C#, etc., which are thus called "strongly typed" languages.
However, almost all the spreadsheet languages are "weakly typed".
a comparison of a string and a numeric value is permitted (returns true of false),
and does not lead to any error.
Even though some meaningless operations show errors such as #VALUE,
they are not blocking and can be easily disregarded by users.
Therefore, our approach aims at applying type checking to spreadsheet programs,
to improve their quality.
Currently, in our type system, we class cell values by the following types:
We implement a set of "dangerous" typing rules in Spreadsheet Verificator.
The tool verifies all the formulas of a spreadsheet,
raises a typing error,
if it discovers a dangerous typing rule may be matched
during the calculation of the spreadsheet.
In the following table, we list the dangerous typing rules
that are easy to formalize.
For instance, "Boolean + | - Currency | Date" means
it is dangerous to add or minus a Boolean value to a Currency or a Date.
| SIN | COS | ATAN | ASIN (Boolean | Date | String) |
| LN | LOG1 | LOG10 | SQRT | EXP (Boolean | Date) |
| -(Boolean | Date) |
| +Boolean |
| POWER | LOG2 (ANY, Boolean | Date) |
| POWER | LOG2 (Boolean | Date, ANY) |
| Currency + | - | * | / Date |
| Date + | - | * | / Currency |
| Currency | Date + | - Boolean |
| Boolean + | - Currency | Date |
| Boolean | String + | - | * | / ANY |
| ANY + | - | * | / Boolean | String |
| Date * | / ANY |
| ANY * | / Date |
| Date < | > | <= | >= | == | <> String | Integer | Double | Boolean | Currency |
| Currency < | > | <= | >= | == | <> String | Boolean | Date |
| String < | > | <= | >= | == | <> Boolean | Integer | Double | Date | Currency |
| Boolean < | > | <= | >= | == | <> String | Integer | Double | Date | Currency |
| Integer | Double < | > | <= | >= | == | <> String | Boolean | Date |
| MIN | MAX (Boolean | String) |
| MIN | MAX has one argument, which is array; the array contains Boolean | String |
| MIN | MAX has one argument, which is array; the array does not contain Boolean | String; it contains Currency | Double | Integer and Date |
| MIN | MAX has more than one argument, and there exists one Boolean | String argument |
| MIN | MAX has more than one argument; there is no Boolean | String argument; there exists one Currency | Double | Integer argument and one Date argument |
| SUM (Boolean | Date | String) |
| SUM has one argument, which is array; the array contains Boolean | Date elements |
| SUM has more than one argument, and there exists one Boolean | Date | String argument |
| AVERAGE | MEDIAN (Boolean | Date | String) |
| AVERAGE | MEDIAN has one argument, which is array; the array contains Boolean | Date elements |
| AVERAGE | MEDIAN has more than one argument, and there exists one Boolean | Date | String argument |
| ... |
Note that some typing rules may be considered dangerous by some users, but safe by others. It is not possible to make a universally absolute and exhaustive set of dangerous typing rules. If you think certain typing rules are missing in the tool, please write to us.
Spreadsheet Verificator is fully automatic;
it does not require users to provide supplementary information to be launched.
Another important advantage of our approach is its "soundness".
That means we guarantee that
none of the dangerous typing rules could ever be matched in any calculation of the spreadsheet.
In other words,
if the spreadsheet is validated by the tool,
the validation applies to all the possible input cell values,
as long as their type does not change.
This is particularly better and more exhaustive than a manually testing approach,
which cannot cover all the possible input instances.
As the cell property (ie, types) we reason on is more abstract and less precise than concrete cell values, verification tools like ours involves a notion of precision.
In case of being not precise enough, there may be false alarms,
which means what the tool raises is not a real error.
For instance, the formula =IF(ABS(A1)>=0, 3, false)+5
always evaluates to 8. Whereas, an analysis solely based on types
translates the formula to "=IF(ABS(A1)>=Integer, Integer, Boolean)+Integer".
As it cannot evaluate the value of "ABS(A1)>=Integer", it considers
the typing error "Boolean+Integer" is possible.
Therefore, one target of verification tools is to improve their precision
and have less false alarms.
- be able to verify array formulas
- verify formulas containing names
- verify VBA macros in a spreadsheet