Added cycle and loop detection for RDG.

Author: LorenzBuehmann

sansa-inference-common/src/main/scala/net/sansa_stack/inference/rules/RuleDependencyGraph.scala

@@ -1,5 +1,6 @@
 package net.sansa_stack.inference.rules
 
+import scala.collection.mutable
 import scalax.collection.Graph
 import scalax.collection.edge.LDiEdge
 import scalax.collection.mutable.DefaultGraphImpl
@@ -48,4 +49,25 @@ class RuleDependencyGraph(iniNodes: Iterable[Rule] = Set[Rule](),
       ))
     )
 
+  /**
+    * Returns all nodes that are connected by an edge to itself.
+    *
+    * @return
+    */
+  def loopNodes(): mutable.Set[NodeBase] = {
+    nodes.filter(n => n.outgoing.map(_.target).contains(n))
+  }
+
+  /**
+    * Returns true if there is a cycle in the graph, i.e. either
+    *
+    * - there is a path n1 -> n2 ->  ... -> n1 or
+    * - a loop, i.e. an edge that connects a vertex to itself.
+    *
+    * @return
+    */
+  def hasCycle(): Boolean = {
+    loopNodes().nonEmpty || findCycle.isDefined
+  }
+
 }

sansa-inference-common/src/main/scala/net/sansa_stack/inference/rules/RuleDependencyGraphGenerator.scala

@@ -7,6 +7,7 @@ import scalax.collection.GraphTraversal.Parameters
 import scalax.collection._
 import scalax.collection.edge.Implicits._
 import scalax.collection.edge._
+import scalax.collection.mutable.DefaultGraphImpl
 
 import org.apache.jena.graph.Node
 import org.apache.jena.reasoner.TriplePattern
@@ -54,6 +55,8 @@ object RuleDependencyGraphGenerator extends Logging {
           g += (r2 ~+> r1) (r2r1.get)
         }
       }
+
+      // cycles?
       val r1r1 = f(r1, r1)
       if (r1r1.isDefined) { // r1 depends on r1, i.e. reflexive dependency
         g += (r1 ~+> r1) (r1r1.get)
@@ -65,7 +68,7 @@ object RuleDependencyGraphGenerator extends Logging {
       g = removeEdgesWithPredicateAlreadyTC(g)
       g = removeCyclesIfPredicateIsTC(g)
       g = removeEdgesWithCycleOverTCNode(g)
-      //      g = prune(g)
+            g = prune(g)
       //      g = prune1(g)
     }
 
@@ -143,10 +146,11 @@ object RuleDependencyGraphGenerator extends Logging {
     ret
   }
 
-
   def prune(graph: RuleDependencyGraph): RuleDependencyGraph = {
     var redundantEdges = Seq[Graph[Rule, LDiEdge]#EdgeT]()
 
+//    graph.outerNodeTraverser.foreach(n => println(n))
+
     // for each node n in G
     graph.nodes.foreach(node => {
       debug("#" * 20)
@@ -216,6 +220,27 @@ object RuleDependencyGraphGenerator extends Logging {
 
   }
 
+  def removeRedundantEdges(graph: RuleDependencyGraph): RuleDependencyGraph = {
+    debug("removeRedundantEdges")
+    var redundantEdges = Seq[Graph[Rule, LDiEdge]#EdgeT]()
+
+    // for each node n in G
+    graph.nodes.foreach(node => {
+      debug("#" * 20)
+      debug(s"NODE:${node.value.getName}")
+
+      // check for nodes that do compute the TC
+      val outgoingEdges = node.outgoing.withFilter(e => e.target != node)
+
+      outgoingEdges.foreach(e => {
+        val targetNode = e.target
+
+      })
+    })
+
+    graph
+  }
+
   // get all nodes that depend on a TC node for a predicate p and another node for p
   def removeEdgesWithPredicateAlreadyTC(graph: RuleDependencyGraph): RuleDependencyGraph = {
     debug("removeEdgesWithPredicateAlreadyTC")
@@ -366,7 +391,7 @@ object RuleDependencyGraphGenerator extends Logging {
   }
 
   def removeCyclesIfPredicateIsTC(graph: RuleDependencyGraph): RuleDependencyGraph = {
-
+    debug("removeCyclesIfPredicateIsTC")
     var redundantEdges = Seq[Graph[Rule, LDiEdge]#EdgeT]()
 
     // for each node n in G
@@ -463,4 +488,6 @@ object RuleDependencyGraphGenerator extends Logging {
     val e = edge.toOuter
     "[" + e.source.getName + " ~> " + e.target.getName + "] '" + e.label
   }
+
+//  override def debug(msg: => String): Unit = println(msg)
 }