XSD: how to restrict number of characters in string type attribute?

You need to create a simple type like so:

  <xs:simpleType name="LimitedString">
    <xs:restriction base="xs:string">
      <xs:maxLength value="50" />
    </xs:restriction>
  </xs:simpleType>

and then use this new type in your schema:

  <xs:complexType name="test">
    <xs:sequence>
      <xs:element name="abc" type="xs:String" />
    </xs:sequence>
    <xs:attribute type="LimitedString" name="myattr" />
  </xs:complexType>

Marc