IS it possible to have a blank date element

Hi
 
I am creating a schema that has amongst its elements a date element ie type
= xs:date. This element is causing me a headache as it is not mandatory. I
have been unable to find a way to allow this element to be left blank (I
have tried setting minOcc to 0 but I get the error "Invalid value for
datatype date"). I am beginning to thing that I will have to create a
default of 9999-01-01 to allow people to skip over this field. Can anyone
tell me different
 
Thanks

Helen 




_______________________________________________________________________ 

The information contained in this email is confidential and is intended 
for the use of the addressee only. Any unauthorised dissemination or 
copying of this email, and any use of disclosure of information 
contained in it, is strictly prohibited and may be illegal. 

Please let us know immediately by telephone if the email has been sent 
to you in error (+44 1481 711166). 
________________________________________________________________________