Hello there,
I think, if you derive your type from xsd:string and then you specify what it should contain in the xsd

attern you'll get what what you're looking for.
For example if I wanted my string to contain things like
<string of lower letters>@<string of lower letters>.com
(as in
ambrosetati@home.com), I could do something like this:
<xsd:element name="myUrl">
<xsd:simpleType>
<xsd:restriction base = "xsd:string">
<xsd

attern value = "([a-z])+@([a-z])+.(com)"/>
</xsd:restriction>
</xsd:simpleType>
</xsd:element>
if you change <xsd

attern value = "([a-z])+@([a-z])+.(com)"/> to
<xsd

attern value = "([a-z])+"/> you'll ensure that it will not be empty and will only contain any combination of letters.
Hope this helps
Ambrose Tati