code: public static PersistenceManager openDB(String dbName) {
      	DBTracer.logCall(ZooJdoHelper.class, dbName); 
      	ZooJdoProperties props = new ZooJdoProperties(dbName);
          PersistenceManagerFactory pmf = JDOHelper.getPersistenceManagerFactory(props);
          PersistenceManager pm = pmf.getPersistenceManager();
          return pm;
      }
docs: Open a database.
  
  This is short for: <br>
  <code>
  ZooJdoProperties props = new ZooJdoProperties(dbName);  <br>
  PersistenceManagerFactory pmf = JDOHelper.getPersistenceManagerFactory(props);  <br>
  PersistenceManager pm = pmf.getPersistenceManager();  <br>
  </code>
  
  @param dbName Name of the database to connect to.
  @return A new PersistenceManager