title: How to build an hierarchy?
body: <p>I want to analyze a piece of document and build an ontology from it.
  There could be many characteristics of this document, and it could be a hierarchy.</p>
  
  <p>What is the best programming method to build this hierarchy with unlimited height?
  A tree?</p>
  
  <p>I am looking for a broad "way" of programming, not necessary code.</p>