By definition, checkbox fields have two values, checked and unchecked. However in reality database technology really has three values under the covers:
There are differences in the way that Not Set and Unchecked are handled internally, but if you adhere to the following way to set and to unset the values of a checkbox, ExtraView will handle the internal differences.
To set a value:
MY_CHECKBOX = 'Y';
To uncheck a value:
MY_CHECKBOX = 'N';
To check whether a checkbox is set:
if (MY_CHECKBOX = 'Y') { ..... };
To check whether a checkbox is not checked:
if (MY_CHECKBOX = 'N') { ..... };
You should not use, or test for the Not Set (sometimes known as the null value) within your rules.