Querying for a set sequence against an XML Document

[manojas]

What is an appropriate query to do this regular expression like
matching on an XML doc
What I DO NOT want to do is use DOM/SAX and process the tree in the
client side

I need to figure out if a sequence of nodes appear in order.
Given an XML
(1)
<Root>
<Data Tag="A"/>
<Node>
<Data Tag="B"/>
.
.
<Data Tag="C"/>
</Node>
<Root>

In the above document (1) the tags {A,B,C} appears in order,hence the
query returns true.In the case below the tags are not inorder
and {C,B,A} hence the query returns false
(2)
<Root>
<Data Tag="C"/>
<Data Tag="B"/>
<Data Tag="A"/>
<Root>

Like the document shown above the nodes neednt be in the same
hierarchy. Also note that I am interested in
a pattern A*B*C, ie the doc below is fine
(3)
<Root>
<Data Tag="A"/>
<Data Tag="B"/>
<Data Tag="D"/>
<Data Tag="C"/>
<Root>


Thanks in advance
Manoj