The following table has been used to initialize the relationship types registry.
+-------------------+---------+--------------------------+ | Relationship Type | Status | Reference | +-------------------+---------+--------------------------+ | CHILD | Current | RFC 5545, Section 3.2.15 | | | | | | PARENT | Current | RFC 5545, Section 3.2.15 | | | | | | SIBLING | Current | RFC 5545, Section 3.2.15 | +-------------------+---------+--------------------------+