org.apache.derby.impl.sql.catalog

Class RoleClosureIteratorImpl

java.lang.Object

org.apache.derby.impl.sql.catalog.RoleClosureIteratorImpl

All Implemented Interfaces:

RoleClosureIterator

public class RoleClosureIteratorImpl
extends java.lang.Object
implements RoleClosureIterator

Allows iterator over the role grant closure defined by the relation GRANT role-a TO role-b, or its inverse.

The graph is represented as a HashMap where the key is the node and the value is a List grant descriptors representing outgoing arcs. The set constructed depends on whether inverse was specified in the constructor.

See Also:

RoleClosureIterator

Method Summary

Modifier and Type	Method and Description
java.lang.String	next() Returns the next (as yet unreturned) role in the transitive closure of the grant or grant-1 relation.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

next

public java.lang.String next()
                      throws StandardException

Description copied from interface: RoleClosureIterator

Returns the next (as yet unreturned) role in the transitive closure of the grant or grant^-1 relation. The grant relation forms a DAG (directed acyclic graph).

 Example:
      Assume a set of created roles forming nodes:
            {a1, a2, a3, b, c, d, e, f, h, j}

      Assume a set of GRANT statements forming arcs:

      GRANT a1 TO b;   GRANT b TO e;  GRANT e TO h;
      GRANT a1 TO c;                  GRANT e TO f;
      GRANT a2 TO c;   GRANT c TO f;  GRANT f TO h;
      GRANT a3 TO d;   GRANT d TO f;  GRANT a1 to j;


          a1            a2         a3
         / | \           |          |
        /  b  +--------> c          d
       j   |              \        /
           e---+           \      /
            \   \           \    /
             \   \---------+ \  /
              \             \_ f
               \             /
                \           /
                 \         /
                  \       /
                   \     /
                    \   /
                      h
 

An iterator on the inverse relation starting at h for the above grant graph will return:

       closure(h, grant-inv) = {h, e, b, a1, f, c, a2, d, a3}
 

An iterator on normal (not inverse) relation starting at a1 for the above grant graph will return:

       closure(a1, grant)    = {a1, b, j, e, h, f, c}
 

Specified by:

next in interface RoleClosureIterator

Returns:

a role name identifying a yet unseen node, or null if the closure is exhausted. The order in which the nodes are returned is not defined, except that the root is always returned first (h and a1 in the above examples).

Throws:

StandardException