[xsl] How to merge XML node including all the corresponding children with unique element and latest value?

Subject: [xsl] How to merge XML node including all the corresponding children with unique element and latest value?
From: Lucent Lau <lucent.lau@xxxxxxxxx>
Date: Mon, 16 Jul 2012 23:54:10 +0700
I have this XSL:
<root>
    <library id="L1">
        <floor1 id="1">
            <shelf id="1">
                <book id="1" action="borrow">
                    <attributes>
                        <user>John</user>
                    </attributes>
                    <other1>y</other1>
                </book>
                <book id="1" action="extend">
                    <attributes>
                        <user>Woo</user>
                        <length>3</length>
                    </attributes>
                    <other2>y</other2>
                </book>
                <book id="2" action="extend">
                    <attributes>
                        <length>2</length>
                        <condition>ok</condition>
                    </attributes>
                    <other3>y</other3>
                </book>
            </shelf>
            <shelf id="2">
        </floor1>
        <floor1 id="2">..</floor1>
    </library>
</root>

Output:
<root>
    <library id="L1">
        <floor1 id="1">
            <shelf id="1">
                <book id="1" action="borrow">
                    <attributes>
                        <user>Woo</user>
                        <length>3</length>
                    </attributes>
                    <other1>y</other1>
                    <other2>y</other2>
                </book>

                <book id="2" action="extend">
                    <attributes>
                        <length>2</length>
                        <condition>ok</condition>
                    </attributes>
                    <other3>y</other3>
                </book>
            </shelf>
            <shelf id="2">
        </floor1>
        <floor1 id="2">..</floor1>
    </library>
</root>

I need to combine the node such that For every node that has the same
id with action=borrow followed by one or more node with action=extend

    Merge it together to the node with action=borrow.
    Merge the attributes children together such that it will have all
the unique attributes from the siblings with the latest value.
    leave other children unchanged

Please let me know how to fix this transformation using XSLT 2.0 ?

Thanks very much.
LL

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