Allows you to build relations between issues. There are two kind of relations. If you had a relation Issue1 and Issue 2 and between Issue 2 and Issue 3. In the normal relation you would see by selected Issue 1 only the Issue 2. In the hierarchical kind you would see a tree with root node Issue 2 and subnote Issue 3. If you select relationship Slave only, so you can would see only the slave items. If you select master and slave, you will see the issues in both direction of relatioship.