I was trying to validate a xml file using xsd wherein a node value should be non-empty. Means there should be atleast one non-whitespace character into that. After lots of googling, I finally wrote up a small pattern to validate that. Here is the fragment.
Define a new type derived from string type and apply the pattern constraint.
<!-- Non-empty string -->
<xs:minLength value="1" />
<xs:pattern value=".*[^\s].*" />
Now use the new type "NonEmptyString" for all the nodes you want to enforce non-empty constraint.