Querying XML Data& using Value method

In querying the XML data we have four methods namely
Querymethod      Returns a fragment of untyped XML
Value method       Returns XML data as a scalar datatype
exists method       Checks whether a certain node exists in the XML data
nodes method       Returns a single column rowset of nodes from the XML column

In Value method,  I tried the value method it gives error?

SELECT BookDetails.value('root/Code','integer') FROM Books
 
Msg 2389, Level 16, State 1, Line 1
XQuery [Books.BookDetails.value()]: 'value()' requires a singleton (or empty sequence), found operand of type 'xs:integer *'

My books Table looks like in attachment
 

This is how Books table was created

CREATE TABLE Books
(
BookID smallint IDENTITY(101,1),
Price smallmoney,
BookDetails XML (BookTypes))


BookDetails is of Type XML and its schema definition follows

-- Creating XML SCHEMA Collection
CREATE XML SCHEMA COLLECTION BookTypes AS '
<schema xmlns="http://www.w3.org/2001/XMLSchema">
<element name="root">
<complexType>
<sequence>
<element name="BookGenere" type="string"/>
<element name="Code" type="integer"/>
</sequence>
</complexType>
</element>
</schema>'



Same is the case with other parameter of BookDetails i.e BookGenere

SELECT BookDetails.value('root/BookGenere','string') FROM Books

Msg 9500, Level 16, State 1, Line 1
The data type 'string' used in the VALUE method is invalid.

In the dfinition is clearly mentioned that its type is integer
And while inserting values also the schema stood by its definition

But when iam trying to retrive the values , its not working
Please help