I had develop an xml schema for checking type of data
as
    <xs:simpleType name="O_FMExchangeRate" xmlns:xs="http://
www.w3.org/2001/XMLSchema">
        <xs:restriction base="xs:float">
            <xs:minExclusive value="0.0000001"/>
            <xs:pattern value="d(0)|\d{1,5}|\d{1,5}\.\d{1,7}|\.\d{1,7}|
\d{1,5}\.|\+\d{1,5}|\+\d{1,5}\.\d{1,7}|\+\.\d{1,7}|\+\d{1,5}\."/>
       </xs:restriction>
    </xs:simpleType>

a problem is that I would like to have this field as an optional
field
but Tag pattern ... d(0)|\ (as above)  didn't help me on that.
do you have any suggestion?