Document is invalid: no grammar found.

Hi, Everyone:
I complied a XML instance : book xml and a schema book.xsd.

In the begining of book.xml, it is like the following:
<?xml version="1.0" encoding="UTF-8"?>
<book isbn="0836217462"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:noNamespaceSchemaLocation="file:book.xsd">

when I run parser with xerces, it always gives error message:

Document is invalid: no grammar found.
What is wrong?

Thanks in advance!
Wenpeng

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