title: What are the known ways to store a tree structure in a relational DB?
body: <p>There is the <a href="http://mikehillyer.com/articles/managing-hierarchical-data-in-mysql/" rel="noreferrer">"put a FK to your parent" method</a>, i.e. each records points to it's parent.<br>
  Which is a hard for read actions but very easy to maintain.</p>
  
  <p>And then there is a "directory structure key" method:</p>
  
  <pre><code>0001.0000.0000.0000 main branch 1
  0001.0001.0000.0000 child of main branch one
  etc
  </code></pre>
  
  <p>Which is super easy to read, but hard to maintain.<br>
  What are the other ways and their cons/pros?</p>