xsd restriction / facets

hello,
    I Need to do something like this:

<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified">
<xsd:element name="XMLMODIFY">

<xsd:complexType>

<xsd:sequence>

<xsd:element name="CUPID" type="cupid"/>

</xsd:sequence>

</xsd:complexType>

</xsd:element>

<xsd:simpleType name="cupid">

<xsd:restriction base="xsd:string">

<xsd:pattern value="[a-z0-9A-Z]*"/>

</xsd:restriction>

</xsd:simpleType>

</xsd:schema>

when I make the xml, i have 2 ways , one with the CUPID node empty, and a second with the CUPID node completed.

If the node cupid is completed i need to validate that the value must be minium of four character and maximum of ten character .

its clear ?

i will aprecciate an answer.

thanks.