Simplify role extraction from axioms

The previous implementation was using the visitor pattern suggested by
the OWLAPI. This was buggy for some reasons and resulting in runtime
exceptions (probably due to the complex class tree of the API). In Scala
using type pattern matching results in a shorter and more readable way
of traversing an AST.

1 files changed, 18 insertions, 58 deletions

diff --git a/src/main/scala/rsacomb/RSAAxiom.scala b/src/main/scala/rsacomb/RSAAxiom.scala
index f504bbe..3cd9a9d 100644
--- a/src/main/scala/rsacomb/RSAAxiom.scala
+++ b/src/main/scala/rsacomb/RSAAxiom.scala
@@ -20,6 +20,7 @@ import org.semanticweb.owlapi.model.{
   OWLClassExpressionVisitorEx
 }
 import org.semanticweb.owlapi.model.OWLObjectProperty
+import scala.collection.JavaConverters._
 
 /* Wrapper trait for the implicit class `RSAAxiom`.
  */
@@ -103,68 +104,27 @@ trait RSAAxiom {
      * of a role if this appears in the axiom (but we will get the role
      * itself instead).
      */
-    private class RSAAxiomRoleExtractor()
-        extends OWLAxiomVisitorEx[List[OWLObjectPropertyExpression]] {
-
-      private class RSAExprRoleExtractor()
-          extends OWLClassExpressionVisitorEx[
-            List[OWLObjectPropertyExpression]
-          ] {
-        override def visit(
-            expr: OWLObjectSomeValuesFrom
-        ): List[OWLObjectPropertyExpression] =
-          List(expr.getProperty)
-
-        override def visit(
-            expr: OWLObjectMaxCardinality
-        ): List[OWLObjectPropertyExpression] =
-          List(expr.getProperty)
-
-        /* NOTE: this instance of `visit` for `OWLClass` shouldn't be necessary. However
-         * if missing, the code throws a `NullPointerException`. It seems like, for some
-         * reason, `OWLClass` is not really a subinterface of `OWLClassExpression`, as
-         * stated in the JavaDocs.
-         */
-        override def visit(expr: OWLClass): List[OWLObjectPropertyExpression] =
-          List()
-
-        def doDefault(
-            expr: OWLClassExpression
-        ): List[OWLObjectPropertyExpression] =
-          List()
-      }
-
-      override def visit(
-          axiom: OWLSubClassOfAxiom
-      ): List[OWLObjectPropertyExpression] = {
-        val visitor = new RSAExprRoleExtractor()
-        val sub = axiom.getSubClass.accept(visitor)
-        val sup = axiom.getSuperClass.accept(visitor)
-        sub ++ sup
+    lazy val objectPropertyExpressionsInSignature
+        : List[OWLObjectPropertyExpression] =
+      axiom match {
+        case a: OWLSubClassOfAxiom =>
+          rolesInExpr(a.getSubClass) ++ rolesInExpr(a.getSuperClass)
+        case a: OWLEquivalentClassesAxiom =>
+          a.getClassExpressions.asScala.toList.flatMap(rolesInExpr(_))
+        case a: OWLSubObjectPropertyOfAxiom =>
+          List(a.getSubProperty, a.getSuperProperty)
+        case _ => List()
       }
 
-      override def visit(
-          axiom: OWLEquivalentClassesAxiom
-      ): List[OWLObjectPropertyExpression] = {
-        // TODO
-        List()
+    private def rolesInExpr(
+        expr: OWLClassExpression
+    ): List[OWLObjectPropertyExpression] =
+      expr match {
+        case e: OWLObjectSomeValuesFrom => List(e.getProperty)
+        case e: OWLObjectMaxCardinality => List(e.getProperty)
+        case _                          => List()
       }
 
-      override def visit(
-          axiom: OWLSubObjectPropertyOfAxiom
-      ): List[OWLObjectPropertyExpression] =
-        List(axiom.getSubProperty(), axiom.getSuperProperty())
-
-      def doDefault(axiom: OWLAxiom): List[OWLObjectPropertyExpression] = List()
-    }
-
-    /* Exposed methods */
-    lazy val objectPropertyExpressionsInSignature
-        : List[OWLObjectPropertyExpression] = {
-      val visitor = new RSAAxiomRoleExtractor()
-      axiom.accept(visitor)
-    }
-
     lazy val toTriple: Option[(OWLClass, OWLObjectProperty, OWLClass)] =
       for {
         subClass <- Some(axiom) collect { case a: OWLSubClassOfAxiom => a }