Adapt LP conversion to RSA check

Part of the process involves the search of unsafe roles in the input
ontology. This is still to be implemented and for now the set of unsafe
roles for the testing example is hardcoded.

4 files changed, 68 insertions, 28 deletions

diff --git a/src/main/scala/rsacomb/RDFoxAxiomConverter.scala b/src/main/scala/rsacomb/RDFoxAxiomConverter.scala
index 3edc908..0a79823 100644
--- a/src/main/scala/rsacomb/RDFoxAxiomConverter.scala
+++ b/src/main/scala/rsacomb/RDFoxAxiomConverter.scala
@@ -1,36 +1,39 @@
 package rsacomb
 
-import org.semanticweb.owlapi.model.{OWLAxiom, OWLSubClassOfAxiom, OWLEquivalentClassesAxiom}
+import org.semanticweb.owlapi.model.{OWLAxiom, OWLSubClassOfAxiom, OWLEquivalentClassesAxiom, OWLObjectPropertyExpression}
 import org.semanticweb.owlapi.model.OWLAxiomVisitorEx
 
 import tech.oxfordsemantic.jrdfox.logic.{Rule, BodyFormula}
 import tech.oxfordsemantic.jrdfox.logic.{Atom, Term, Variable, Literal}
+import tech.oxfordsemantic.jrdfox.logic.{TupleTableName}
 
 import scala.collection.JavaConverters._
 
 import rsacomb.SkolemStrategy
 import rsacomb.RDFoxRuleShards
 import org.semanticweb.owlapi.model.OWLSubObjectPropertyOfAxiom
+import org.semanticweb.owlapi.model.OWLObjectProperty
 
 object RDFoxAxiomConverter {
 
-  def apply(term : Term, skolem : SkolemStrategy) : RDFoxAxiomConverter =
-        new RDFoxAxiomConverter(term, skolem)
-
-  def apply(term : Term) : RDFoxAxiomConverter =
-        new RDFoxAxiomConverter(term, SkolemStrategy.None)
+  def apply(
+    term : Term = Variable.create("x"),
+    skolem : SkolemStrategy = SkolemStrategy.None,
+    unsafe : List[OWLObjectPropertyExpression] = List()
+  ) : RDFoxAxiomConverter =
+          new RDFoxAxiomConverter(term, skolem, unsafe)
 
 } // object RDFoxAxiomConverter
 
-class RDFoxAxiomConverter(term : Term, skolem : SkolemStrategy)
+class RDFoxAxiomConverter(term : Term, skolem : SkolemStrategy, unsafe : List[OWLObjectPropertyExpression])
   extends OWLAxiomVisitorEx[List[Rule]]
 {
 
   override
   def visit(axiom : OWLSubClassOfAxiom) : List[Rule] = {
     // Skolemization is needed only for the head of an axiom
-    val subVisitor = new RDFoxClassExprConverter(term,SkolemStrategy.None)
-    val superVisitor = new RDFoxClassExprConverter(term, skolem)
+    val subVisitor = new RDFoxClassExprConverter(term,SkolemStrategy.None, unsafe)
+    val superVisitor = new RDFoxClassExprConverter(term, skolem, unsafe)
     // Each visitor returns a `RDFoxRuleShards`, a tuple (res,ext):
     // - the `res` List is a list of atoms resulting from the conversion
     //   of the axiom.
diff --git a/src/main/scala/rsacomb/RDFoxClassExprConverter.scala b/src/main/scala/rsacomb/RDFoxClassExprConverter.scala
index 58bee44..227c25b 100644
--- a/src/main/scala/rsacomb/RDFoxClassExprConverter.scala
+++ b/src/main/scala/rsacomb/RDFoxClassExprConverter.scala
@@ -10,14 +10,17 @@ import tech.oxfordsemantic.jrdfox.logic.{Atom, Term, Variable, Literal, Datatype
 
 import rsacomb.SkolemStrategy
 import rsacomb.RDFoxRuleShards
+import org.semanticweb.owlapi.model.OWLObjectPropertyExpression
+import org.semanticweb.owlapi.model.OWLObjectProperty
 
 object RDFoxClassExprConverter {
 
-  def apply(term : Term, skolem : SkolemStrategy) : RDFoxClassExprConverter =
-        new RDFoxClassExprConverter(term, skolem)
-
-  def apply(term : Term) : RDFoxClassExprConverter =
-        new RDFoxClassExprConverter(term, SkolemStrategy.None)
+  def apply(
+    term : Term = Variable.create("x"),
+    skolem : SkolemStrategy = SkolemStrategy.None,
+    unsafe : List[OWLObjectPropertyExpression] = List()
+  ) : RDFoxClassExprConverter =
+          new RDFoxClassExprConverter(term, skolem, unsafe)
 
   def merge(rules : List[RDFoxRuleShards]) : RDFoxRuleShards = {
     rules.foldLeft(RDFoxRuleShards(List(),List())) {
@@ -31,7 +34,7 @@ object RDFoxClassExprConverter {
 
 } // object RDFoxClassExprConverter
 
-class RDFoxClassExprConverter(term : Term, skolem : SkolemStrategy)
+class RDFoxClassExprConverter(term : Term, skolem : SkolemStrategy, unsafe : List[OWLObjectPropertyExpression])
   extends OWLClassExpressionVisitorEx[RDFoxRuleShards]
 {
 
@@ -46,7 +49,7 @@ class RDFoxClassExprConverter(term : Term, skolem : SkolemStrategy)
   // OWLObjectIntersectionOf
   override
   def visit(expr : OWLObjectIntersectionOf) : RDFoxRuleShards = {
-    val visitor = new RDFoxClassExprConverter(term,skolem)
+    val visitor = new RDFoxClassExprConverter(term, skolem, unsafe)
     // TODO: maybe using `flatMap` instead of `merge` + `map` works as well
         RDFoxClassExprConverter.merge (
       expr.asConjunctSet.asScala.toList
@@ -75,22 +78,33 @@ class RDFoxClassExprConverter(term : Term, skolem : SkolemStrategy)
     // TODO: variables needs to be handled at visitor level. Hardcoding
     // the name of the varibles might lead to errors for complex cases.
     val y = Variable.create("y")
-    val (fun,term1) = skolem match {
-        case SkolemStrategy.None => (List(),y)
-        case SkolemStrategy.Constant(c) => (List(), Literal.create(c, Datatype.IRI_REFERENCE))
+    val prop = expr.getProperty()
+    // Computes the result of rule skolemization. Depending on the used 
+    // technique it might involve the introduction of additional atoms,
+    // and/or fresh constants and variables.
+    val (head, body, term1) = skolem match {
+        case SkolemStrategy.None => (List(), List(), y)
+        case SkolemStrategy.Constant(c) => (List(), List(), Literal.create(c, Datatype.IRI_REFERENCE))
+        case SkolemStrategy.ConstantRSA(c) => {
+          val lit = Literal.create(c, Datatype.IRI_REFERENCE)
+          if (unsafe.contains(prop))
+            (List(Atom.create(TupleTableName.create("internal:PE"),term,lit), Atom.create(TupleTableName.create("internal:U"),lit)), List(), lit)
+          else 
+            (List(), List(), lit)
+        }
         case SkolemStrategy.Standard(f) => 
           // At the time of writing the RDFox library does not have a
           // particular class for the "SKOLEM" operator and it is instead
-          // a simple builtin function with a special name.
-          (List(BindAtom.create(BuiltinFunctionCall.create("SKOLEM",term),y)),y)
+          // a simple builtin function with a "special" name.
+          (List(),List(BindAtom.create(BuiltinFunctionCall.create("SKOLEM",term),y)),y)
     }
-    val classVisitor = new RDFoxClassExprConverter(term1,skolem)
+    val classVisitor = new RDFoxClassExprConverter(term1, skolem, unsafe)
     val classResult = expr.getFiller.accept(classVisitor)
     val propertyVisitor = new RDFoxPropertyExprConverter(term, term1, skolem)
     val propertyResult = expr.getProperty.accept(propertyVisitor)
     RDFoxRuleShards(
-      classResult.res ++ propertyResult,
-      fun ++ classResult.ext
+      classResult.res ++ propertyResult ++ head,
+      classResult.ext ++ body
     )
   }
 
@@ -100,7 +114,7 @@ class RDFoxClassExprConverter(term : Term, skolem : SkolemStrategy)
     // TODO: again, no hardcoded variables
     val vars = List(Variable.create("y"),Variable.create("z"))
     val classResult = RDFoxClassExprConverter.merge(
-      vars.map(new RDFoxClassExprConverter(_,skolem))
+      vars.map(new RDFoxClassExprConverter(_,skolem, unsafe))
           .map(expr.getFiller.accept(_))
     )
     val propertyResult = 
diff --git a/src/main/scala/rsacomb/RSAComb.scala b/src/main/scala/rsacomb/RSAComb.scala
index a6f237f..62414e9 100644
--- a/src/main/scala/rsacomb/RSAComb.scala
+++ b/src/main/scala/rsacomb/RSAComb.scala
@@ -10,7 +10,9 @@ import org.semanticweb.owlapi.model.{OWLAxiom, OWLSubClassOfAxiom, OWLEquivalent
 import org.semanticweb.owlapi.model.OWLClassExpression
 import org.semanticweb.owlapi.model.OWLOntology
 import org.semanticweb.owlapi.model.OWLOntologyManager
+import org.semanticweb.owlapi.model.IRI
 import org.semanticweb.owlapi.model.parameters.Imports
+import uk.ac.manchester.cs.owl.owlapi.OWLObjectPropertyImpl
 
 import tech.oxfordsemantic.jrdfox.Prefixes
 import tech.oxfordsemantic.jrdfox.client.{ConnectionFactory, ServerConnection, DataStoreConnection}
@@ -55,6 +57,11 @@ object RSA {
 
     val renderer = new DLSyntaxObjectRenderer()
 
+    // Here we need to compute the unsafe roles. This is hardcoded for now.
+    val unsafe = List(
+      new OWLObjectPropertyImpl(IRI.create("http://example.com/rsa_example.owl#S")).getInverseProperty()
+    )
+
     /* Print TBox axioms */
     println("TBox/RBox:")
     for {
@@ -68,12 +75,12 @@ object RSA {
     println("Logic rules:")
     for {
       axiom <- onto.tboxAxioms(Imports.EXCLUDED).collect(Collectors.toList()).asScala
-      visitor = new RDFoxAxiomConverter(Variable.create("x"), SkolemStrategy.Constant(axiom.toString))
+      visitor = new RDFoxAxiomConverter(Variable.create("x"), SkolemStrategy.ConstantRSA(axiom.toString), unsafe)
       rule  <- axiom.accept(visitor)
     } yield println(rule)
     for {
       axiom <- onto.rboxAxioms(Imports.EXCLUDED).collect(Collectors.toList()).asScala
-      visitor = new RDFoxAxiomConverter(Variable.create("x"), SkolemStrategy.Constant(axiom.toString))
+      visitor = new RDFoxAxiomConverter(Variable.create("x"), SkolemStrategy.ConstantRSA(axiom.toString), unsafe)
       rule  <- axiom.accept(visitor)
     } yield println(rule)
 
diff --git a/src/main/scala/rsacomb/SkolemStrategy.scala b/src/main/scala/rsacomb/SkolemStrategy.scala
index 9df167f..bcf6828 100644
--- a/src/main/scala/rsacomb/SkolemStrategy.scala
+++ b/src/main/scala/rsacomb/SkolemStrategy.scala
@@ -29,7 +29,7 @@ object SkolemStrategy {
     def genFunctionString(str : String) = "f_" ++ str.hashCode.toString
   }
 
-  /* Functional skolemization
+  /* Constant skolemization
    *
    * From 
    *    A ⊑ ∃R.B
@@ -42,5 +42,21 @@ object SkolemStrategy {
     def apply(axiom : String) = new Constant(genConstantString(axiom))
     def genConstantString(str : String) = "internal:c_" ++ str.hashCode.toString
   }
+
+  /* (RSA) Constant skolemization
+   * This is a special skolemization option to introduce additional atoms for RSA
+   * checking algorithm.
+   *
+   * From 
+   *    A ⊑ ∃R.B
+   * to
+   *    A(y) -> R(x,c), PE(x,c), B(c)
+   * for c, fresh constant associated with the input axiom and PE an internal predicate.
+   */
+  case class ConstantRSA(const : String) extends SkolemStrategy
+  object ConstantRSA {
+    def apply(axiom : String) = new ConstantRSA(genConstantString(axiom))
+    def genConstantString(str : String) = "internal:c_" ++ str.hashCode.toString
+  }
 }