If you are working with Infopath 2007 (maybe together with SharePoint 2007) and if you are creating
a new form, you often need fields which are mandatory.
Sometimes it happens, that a specifc field should be mandatory, just if another field (for example a checkbox,
or a specific field within a dropdown menu) is selected (or another textbox isn't empty for example).
If you know how, it's easy to create such a rule
All what you need is to create a rule (see picture), which validates the field (which is related to the "optional"
mandatory field) if it is checked or not. Of course you can also connect the "optional" mandatory
field (in our case the address field) to a drop down box for example.