4.5. Deleting a role instance
Much like when we remove a context instance, we have to consider the case of removing a role instance. How does the PDR ensure that requests that are affected by this change, are updated?
Figure 4. All ways to visit a role. Red parts will disappear when the role instance is removed.
From Figure 4 we learn that there are three ways for a query to alight on a role instance node. When that node is removed, all queries with such steps (the green lines) should be recomputed.
Shouldn’t we recompute queries that have one of the inverses of these steps? Just think how such a query would arrive at R1 in the first place: it can only be by one of steps illustrated by green lines. Hence, if we find all queries with the green steps, we’ve got them all.