Hi, 

I'm having some trouble with designing an XML document/vocabulary.

Situation:

I have sets of numerical data, that is essentially tabular data captured in 
xml elements:

<dataset id='1'>
<row/>
<row/>
<row/>
<dataset>
<dataset id='2'>
...
...
</dataset>
...

PROBLEM:
I need to extend this with xml that captures multiple hierarchical 
relationships between these datasets. Currently I've defined a 
<datahierarchy/> element that captures a single type of relationship between 
the datasets:

<datahierarchy>
<tier id='1'>
<dataset>1</dataset>
<dataset>2</dataset>

<tier id='2'>
<dataset>3</dataset>
</tier>
</tier>
...
</datahierarchy>

However, the datasets have several different hierarchal relationships. i.e. 
where <dataset id='3'> may be the root rather than a child, and have <dataset 
id='2'> and <dataset id='1'> as children. 

The easy solution would be to capture the different types of data 
hierarchies in multiple <datahierarchy></datahierarchy> elements. But I am 
reluctant to do this because it seems like a clumsy and spactially expensive 
solution. 

Any ideas on how I could capture the hierarchy and relationships of my 
datasets in xml? 

Could someone provide links to tutorials regarding xml design? I've googled 
it with very little sucess.

Thanks.