PMCB's node_match pathing question

[williampma]

Anyone know why didn't this pattern in the test match to anything?

https://github.com/opencog/atomspace/blob/8112ab7731bea56a635d402bac80d46ebea5b94c/tests/query/MissingUTest.cxxtest

I overwrote node_match to allow any node to match to VariableNode, so this should results in (ConceptNode "John") being matched to (VariableNode "$Z"), but the Pattern Matcher didn't even go into the node_match callback and produced no grounding.

It only does this in some cases. For example, with the current bc-example.scm (https://github.com/opencog/atomspace/blob/master/tests/rule-engine/bc-example.scm) searching

(ImplicationLink
 (VariableNode "$A")
 (InheritanceLink
  (ConceptNode "Fritz")
  (ConceptNode "green")
  )
)

can match (ConceptNode "Fritz") to (VariableNode "$Z"). However, as soon as I changed to search for a non-existence name

(ImplicationLink
 (VariableNode "$A")
 (InheritanceLink
  (ConceptNode "RandomName")
  (ConceptNode "green")
  )
)

it fails to match to (VariableNode "$Z"). Not sure if there's something I am not seeing with the pattern. Maybe some path exploration problem that only happens on some rare instances when a node is to be matched to another node that is already wrapped by another VariableNode?

[leungmanhin]

Perhaps it started with (ConceptNode "RandomName") and couldn't find any of its incoming set (because it did not exist) so the search ended that way before going to any callback?

[williampma]

Ah, right, that makes sense. I completely forgot about those starting criteria. I should be looking at those method then. Thanks!