254 13 Local, Global and Glocal Knowledge Representation
The asymmetric HebbianLink indicates that when the first argument is present in a situation, the second is also often present. The symmetric (default) version indicates that this relationship holds in both directions. The inverse versions indicate the negative relationship: e.g. when one argument is present in a situation, the other argument is often not present.
13.3.6 Procedure Nodes
There are nodes representing various sorts of procedures; these are kinds of ProcedureNode, e.g.
e SchemaNode, indicating any procedure
e GroundedSchemaNode, indicating any procedure associated in the system with a Combo program or C++ function allowing the procedure to be executed
e PredicateNode, indicating any predicate that associates a list of arguments with an output truth value
e GroundedPredicateNode, indicating a predicate associated in the system with a Combo program or C++ function allowing the predicate’s truth value to be evaluated on a given specific list of arguments
ExecutionLinks and EvaluationLinks record the activity of SchemaNodes and PredicateN- odes. We have seen many examples of EvaluationLinks in the above. Example ExecutionLinks would be:
ExecutionLink step\_forward ExecutionLink step\_forward 5 ExecutilonLink + ListLink NumberNode: 2 NumberNode: 3
The first example indicates that the schema "step forward" has been executed. The second example indicates that it has been executed with an argument of "5" (meaning, perhaps, that 5 steps forward have been attempted). The last example indicates that the "++" schema has been executed on the argument list (2,3), presumably resulting in an output of 5. The output of a schema execution may be indicated using an ExecutionOutputLink, e.g.
ExecutilonOutput Link
+
ListLink
NumberNode: 2 NumberNode: 3
refers to the value "5" (as a NumberNode).
13.3.7 Links for Special External Data Types
Finally, there are also Atom types referring to specific types of data important to using OpenCog in specific contexts.
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