Microsoft is developing a programming system that makes
it easier to manipulate trees.

Let's learn from this for the requirements of our project.

XLinq
.NET Language Integrated Query
for XML Data
September 2005


3.1.2 XML Query Extensions
XML-specific query extensions provide you with the query operations 
you would expect when working in an XML tree data structure. 
These XML-specific query extensions are analogous to the XPath axes. 
For example, the Elements method is equivalent to the 
XPath * (star) operator. The following sections describe each of 
the XML-specific query extensions in turn.

3.1.2.2 Descendants and Ancestors
The Descendants and Ancestors query operators let you query down and 
up the XML tree, respectively. Descendants with no parameters 
gives you all the child content of an XElement and, in turn, 
each child's content down to the leaf nodes (the XML subtree). 
Optionally, you can specify an XName (Descendants(XName)) 
and retrieve all of the descendants with a specific name, 
or specify a type (Descendants<T>) and retrieve all of the 
descendants of a specified XLinq type (for example, XComment).  
For example, to get all of the phone numbers in our contact list, 
you could do the following:

contacts.Descendants("phone");

Descendants and Ancestors do not include the current node.  
If you use Descendants() on the root element, you will get the 
entire XML tree except the root element. If you want to include the 
current node, use SelfAndDescendants, which lets you specify an 
XName or type.

Ancestors and SelfAndAncestors work similarly to Descendants and 
SelfAndDescendants; they just go up the XML tree instead of down. 

The Descendants and Ancestors XML query extensions can greatly 
reduce the code needed to traverse an XML tree. You will find that 
you use them often for quick navigation in an XML tree.

Implications for project requirement:

A // * : entire object, including root (SelfAndDescendants)
A // B : all B descendants (SelfAndDescendants)
A // -> *,phone,* : all descendants having a phone field, including
         the target of the phone field (SelfAndDescendants)