Counting items related by a linked list

I have the following type of xml document:
Note:
1) All IDs are unique and can be any positive number
2) The link pairs below can link any item to any different Item.
3) CItems are always in the "Target" portion of the link table.
4) No item can be linked more than once to another item.

<AItem>
  <ID=1/>
  <Name=/>
</AItem>
<AItem>
  <ID=2/>
  <Name=/>
</AItem>
<AItem>
  <ID=3/>
  <Name=/>
</AItem>
<AItem>
  <ID=4/>
  <Name=/>
</AItem>
<AItem>
  <ID=5/>
  <Name=/>
</AItem>

<BItem>
  <ID=101/>
  <Name=/>
</BItem>
<BItem>
  <ID=102/>
  <Name=/>
</BItem>
<BItem>
  <ID=103/>
  <Name=/>
</BItem>
<BItem>
  <ID=104/>
  <Name=/>
</BItem>
<BItem>
  <ID=105/>
  <Name=/>
</BItem>
<BItem>
  <ID=106/>
  <Name=/>
</BItem>

<CItem>
  <ID=1001/>
  <Name=/>
</CItem>
<CItem>
  <ID=1002/>
  <Name=/>
</CItem>
<CItem>
  <ID=1003/>
  <Name=/>
</CItem>
<CItem>
  <ID=1004/>
  <Name=/>
</CItem>
<CItem>
  <ID=1005/>
  <Name=/>
</CItem>
<CItem>
  <ID=1006/>
  <Name=/>
</CItem>
<CItem>
  <ID=1007/>
  <Name=/>
</CItem>

<LinkItem>
  <SourceID>4</SourceID>
  <TargetID>1003</TargetID>
</LinkItem>
<LinkItem>
  <SourceID>6</SourceID>
  <TargetID>1003</TargetID>
</LinkItem>
<LinkItem>
  <SourceID>105</SourceID>
  <TargetID>1002</TargetID>
</LinkItem>
<LinkItem>
  <SourceID>3</SourceID>
  <TargetID>101</TargetID>
</LinkItem>
<LinkItem>
  <SourceID>4</SourceID>
  <TargetID>1003</TargetID>
</LinkItem>
<LinkItem>
  <SourceID>102</SourceID>
  <TargetID>1</TargetID>
</LinkItem>
<LinkItem>
  <SourceID>101</SourceID>
  <TargetID>1003</TargetID>
</LinkItem>