tentando transformar XML em tabelas SQL hierárquicas, alguém pode fornecer uma boa explicação de duas partes deste exemplo de código?

Estou tentando aprender como transformar XML em tabelas SQL hierárquicas.

Encontrei um trecho de código antigo de um fórum da Microsoft que é basicamente o que estou tentando fazer, mas gostaria de saber se alguém poderia ajudar a descobrir o que está acontecendo linha por linha neste código, principalmente depois que o xml foi carregado no @XML

--I understand this part, just making the tables  

DECLARE @Books TABLE (BookID int identity(1,1),BookTitle varchar(50),BookLanguage varchar(20),BookPrice decimal(18,2))  
DECLARE @Topics TABLE (TopicID int identity(1,1),BookID int,TopicTitile varchar(50),Page int)  

--I understand this part, defining the @xml variable to be the xml below.. just a usual xml...


DECLARE @xml XML  
SET @xml = '  
<bookstore>  
    <name>My Bookstore</name><br/>  
    <location>New York</location><br/>  
    <book>  
        <title lang=&quot;eng&quot;>Harry Potter</title>  
        <price>29.99</price>  
        <tableOfContents>  
            <topic>  
                <title>Harry Potter Topic 1</title>  
                <page>2</page>  
            </topic>  
            <topic>  
                <title>Harry Potter Topic 2</title>
                <page>5</page>
            </topic>
        </tableOfContents>
    </book>
    <book>
        <title lang=&quot;eng&quot;>Learning XML</title>
        <price>39.95</price>
        <tableOfContents>
            <topic>
                <title>Learning XML Topic 1</title>
                <page>1</page>
            </topic>
            <topic>
                <title>Learning XML Topic 2</title>
                <page>2</page>
            </topic>
        </tableOfContents>
    </book>
</bookstore>'



--what is going on below here?  I am familiar with inserting data into tables,  
--but what kind of insert is this where you are selecting some things and then doing a  
--from @xml.nodes also, what is that T(c) at the end?  and do we always have to put    
--a [1] after each xml element to denote we are referring to the first one we encounter?  


INSERT INTO @Books  
SELECT T.c.value('title[1]','varchar(50)') AS 'BookTitle',  
    T.c.value('(title/@lang)[1]','varchar(20)') AS 'BookLanguage',  
    T.c.value('price[1]','decimal(18,2)') AS 'BookPrice'  
FROM @xml.nodes('/bookstore/book') T(c)  


--what is going on here as well?  what is n(x) ? 
--could you explain this line by line-ish as well? I ran this on  
--SQL Server Management Studio and noticed that both of the 'topic titles' for each  
--book got inserted.  Where in the code did those get put into the table?

INSERT INTO @Topics  
SELECT b.BookID,n.x.value('title[1]','varchar(50)') AS 'TopicTitile',  
    n.x.value('page[1]','int') AS 'TopicPage'  
FROM @Books b   
cross apply @xml.nodes('/bookstore/book/tableOfContents/topic[../../title=sql:column("b.BookTitle")]') n(x)  


--below here is just regular sql selects so this makes sense.  

SELECT BookID,BookTitle,BookLanguage,BookPrice FROM @Books  
SELECT TopicID,BookID,TopicTitile,Page FROM @Topics  

O fórum ao qual eu estava me referindo e tentando aprender com o post antigo é:

http://social.msdn.microsoft.com/Forums/en/sqlxml/thread/7216ccc9-c1d7-418d-95a2-ec3a96de2c27