title: Why should I avoid loops when designing relationships for a database?
body: <p>Someone told me that it was bad design to have loops in the datamodel. I have heard this before a couple of times but didn't pay much attention. For example you have entities User, Project, Activity. A project is owned by a User, so we have a one-to-many relationship from user to Project. An activity can be assigned to a single User, another one-to-many relationship from User to Activity. Of course a project is defined by a set of activities, another one-to-many relationship from Project to Activity. Thus a loop is formed.</p>
  
  <p>I asked this guy why is it bad design but he told me he didn't know either, he was told so too, monkey learning at it's best.</p>
  
  <p>I tried searching but I guess I didn't use the proper words, however this seems  to me something that should be fundamental for someone trying to design a DB.</p>
  
  <p>So, can anyone point me to some useful info about loops/cycles in er/db diagrams, should they be avoided?</p>