SQL 错误: ORA-31000: 资源 'http://xmlbook.com/sample/contact.xsd' 不是 XDB 方案文档

现已通过
BEGIN
DBMS_XMLSCHEMA.registerSchema('http://www.xmlbook.com/sample/contact.xsd',
xdburitype('/public/test/contact.xsd'),
genTypes => FALSE, 
genTables => FALSE,
options => DBMS_XMLSCHEMA.REGISTER_BINARYXML);
END;
/
注册了XML模式，通过如下select语句，查询证明注册成功select schema_url,local
from user_xml_schemas
order by schema_urlSCHEMA_URL                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
http://www.xmlbook.com/sample/contact.xsd    但现在通过create table语句创建xmltype类型的表出现错误CREATE TABLE contact_xsxtbl OF XMLTYPE
XMLTYPE STORE AS SECUREFILE BINARY XML
XMLSCHEMA "http://xmlbook.com/sample/contact.xsd" ELEMENT "contact";命令出错, 行: 1 列: 0
错误报告:
SQL 错误: ORA-31000: 资源 'http://xmlbook.com/sample/contact.xsd' 不是 XDB 方案文档
31000. 00000 -  "Resource '%s' is not an XDB schema document"
*Cause:    The given schema URL does not refer to a registered XDB schema
*Action:   Make sure the specified schema has been registered in XDB为什么已经注册成功了，还会出现错误我查了一下，我的XDB的状态是valid，请大家帮助，谢谢了