It's also common to want to compute the transitive closure of these relations, for instance, in listing all the issues that are, transitively, duped to the current one to hunt for information about how to reproduce them.

The parent/child relation is obviously a transitive, but "duplicate of" may be transitive too, but other relations like "related to" may not be transitive.

some of its properties needs to be specified, like whether the relation is transitive, so filtering can include or exclude issues related to related issues. For example when I want to see issues blocked by given issue, a filter needs to calculate transitive closure (recursively expand the relation on related issues until all reachable issues are found). On the other side, issue may be related to a second issue, but not to the third issue to which the second issue is related to.