Restrict the length of the data to the maximum number of XML characters allowed when set on a BDL STRING, VARCHAR, CHAR or TEXT, or the number of bytes allowed when set on a BDL BYTE.
DEFINE myStr STRING ATTRIBUTES(XSDString, XSDMaxLength="12", XMLName="MyString")
DEFINE myByte BYTE ATTRIBUTES(XSDBase64Binary, XSDMaxLength="8000", XMLName="MyPicture")