An element with any type of child elements except empty string - xsd-validation

Question

I have very little knowledge in xsd and in an urgent need for a solution to a petty problem.
I need to define an element(named tag) which may have any type and number of child elements(and texts as well) but must not contain an empty string.
Example: <tag1> co<sub1>2</sub1> <b1>laser</b1></tag1>,<tag1>co2</tag1>,<tag1><i1>laser</i1></tag1> are allowed (let's say that even <tag1><i1></i1></tag1> is also allowed). But <tag1></tag1> not allowed. Please let me know if there is a very simple way of doing this.

Answer 1

If you are using XSD 1.1, you can use an assertion to check the condition you describe:
<xs:element name="tag" type="non-empty"/>
<xs:complexType name="non-empty">
<xs:sequence minOccurs="0" maxOccurs="unbounded">
<xs:any/>
</xs:sequence>
<xs:assert test="child::* or not(string(.) eq '')"/>
</xs:complexType>
In XSD 1.0, there isn't quite such a simple approach; if I were you and working in XSD 1.0, I'd change the design to something easier to express in XSD 1.0.
In 1.0, it's easy to require that the tag element have one or more children, without constraining the children:
<xs:complexType name="non-empty" mixed="true">
<xs:sequence minOccurs="1" maxOccurs="unbounded">
<xs:any/>
</xs:sequence>
</xs:complexType>
<xs:element name="tag" type="non-empty"/>
It's also easy to specify that the tag element can have any non-empty string (I'm taking you at your word here, and allowing strings consisting only of white space -- be careful what you ask for):
<xs:simpleType name="non-empty">
<xs:restriction base="xs:string">
<xs:minLength value="1"/>
</xs:restriction>
</xs:simpleType>
<xs:element name="tag" type="non-empty"/>
What's not possible in 1.0 is (a) declaring an element as having either a simple or a complex type, or (b) constraining the textual content of a complex type with mixed content.
Good luck.