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diff --git a/src/main/scala/uk/ac/ox/cs/rsacomb/ontology/Ontology.scala b/src/main/scala/uk/ac/ox/cs/rsacomb/ontology/Ontology.scala
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+/*
+ * Copyright 2020, 2021 KRR Oxford
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package uk.ac.ox.cs.rsacomb.ontology
+
+import java.io.File
+import java.util.stream.Collectors
+
+import scala.collection.mutable.Map
+import scala.collection.JavaConverters._
+import scalax.collection.Graph
+import scalax.collection.GraphPredef._, scalax.collection.GraphEdge._
+
+import org.semanticweb.owlapi.model.parameters.Imports
+import org.semanticweb.owlapi.apibinding.OWLManager
+import org.semanticweb.owlapi.model.{OWLOntology, OWLAxiom, OWLLogicalAxiom}
+import org.semanticweb.owlapi.model.{OWLObjectPropertyExpression}
+import org.semanticweb.owlapi.reasoner.structural.StructuralReasonerFactory
+import tech.oxfordsemantic.jrdfox.logic.datalog.Rule
+import tech.oxfordsemantic.jrdfox.logic.expression.{Resource, Term, Variable}
+
+import uk.ac.ox.cs.rsacomb.approximation.Approximation
+import uk.ac.ox.cs.rsacomb.converter._
+import uk.ac.ox.cs.rsacomb.suffix._
+import uk.ac.ox.cs.rsacomb.util.{RDFoxUtil, RSA}
+
+import uk.ac.ox.cs.rsacomb.RSAUtil
+
+object Ontology {
+
+  /** Simplify conversion between Java and Scala collections */
+  import uk.ac.ox.cs.rsacomb.implicits.JavaCollections._
+
+  /** Type wrapper representing a dependency graph for the ontology.
+    *
+    * The graph is returned along with a map associating each node (IRI
+    * string of the resource), with the corresponding axiom in the
+    * original TBox.
+    */
+  type DependencyGraph = (Graph[Resource, DiEdge], Map[String, OWLAxiom])
+
+  /** Manager instance to interface with OWLAPI
+    *
+    * TODO: turn this into an implicit class parameter.
+    */
+  val manager = OWLManager.createOWLOntologyManager()
+
+  /** Compute the RSA dependency graph for a set of axioms
+    *
+    * @param axioms set of input axioms (TBox) to build the dependency
+    * graph.
+    * @param datafiles data (ABox) to build the dependency graph.
+    * @param unsafe list of unsafe roles in the TBox.
+    *
+    * @return a tuple containing the dependency graph and a map between
+    * the newly introduced constants and the corresponding input axioms.
+    *
+    * @note no check on the ontology language is performed since the
+    * construction of the dependency graph is computed regardless. The
+    * input axioms are assumed to be normalized.
+    */
+  def dependencyGraph(
+      axioms: List[OWLLogicalAxiom],
+      datafiles: List[File],
+      unsafe: List[OWLObjectPropertyExpression]
+  ): DependencyGraph = {
+
+    var nodemap = Map.empty[String, OWLAxiom]
+
+    /* Create custom converter */
+    object RSAConverter extends RDFoxConverter {
+
+      import org.semanticweb.owlapi.model.{
+        OWLClassExpression,
+        OWLObjectSomeValuesFrom,
+        OWLDataSomeValuesFrom
+      }
+
+      override def convert(
+          expr: OWLClassExpression,
+          term: Term,
+          unsafe: List[OWLObjectPropertyExpression],
+          skolem: SkolemStrategy,
+          suffix: RSASuffix
+      ): Shards =
+        (expr, skolem) match {
+
+          case (e: OWLObjectSomeValuesFrom, c: Constant) => {
+            nodemap.update(c.iri.getIRI, c.axiom)
+            val (res, ext) = super.convert(e, term, unsafe, skolem, suffix)
+            if (unsafe contains e.getProperty)
+              (RSA.PE(term, c.iri) :: RSA.U(c.iri) :: res, ext)
+            else
+              (RSA.PE(term, c.iri) :: res, ext)
+          }
+
+          case (e: OWLDataSomeValuesFrom, c: Constant) => {
+            nodemap.update(c.iri.getIRI, c.axiom)
+            val (res, ext) = super.convert(e, term, unsafe, skolem, suffix)
+            if (unsafe contains e.getProperty)
+              (RSA.PE(term, c.iri) :: RSA.U(c.iri) :: res, ext)
+            else
+              (RSA.PE(term, c.iri) :: res, ext)
+          }
+
+          case _ => super.convert(expr, term, unsafe, skolem, suffix)
+        }
+    }
+
+    /* Ontology convertion into LP rules */
+    val term = RSAUtil.genFreshVariable()
+    val result = axioms.map(a =>
+      RSAConverter.convert(a, term, unsafe, new Constant(a), Empty)
+    )
+
+    val datalog = result.unzip
+    val facts = datalog._1.flatten
+    var rules = datalog._2.flatten
+
+    /* Open connection with RDFox */
+    val (server, data) = RDFoxUtil.openConnection("rsa_dependency_graph")
+
+    /* Add additional built-in rules */
+    val varX = Variable.create("X")
+    val varY = Variable.create("Y")
+    rules = Rule.create(
+      RSA.E(varX, varY),
+      RSA.PE(varX, varY),
+      RSA.U(varX),
+      RSA.U(varY)
+    ) :: rules
+    /* Load facts and rules from ontology */
+    RDFoxUtil.addFacts(data, facts)
+    RDFoxUtil.addRules(data, rules)
+    /* Load data files */
+    RDFoxUtil.addData(data, datafiles: _*)
+
+    /* Build the graph */
+    val query = "SELECT ?X ?Y WHERE { ?X rsa:E ?Y }"
+    val answers = RDFoxUtil.submitQuery(data, query, RSA.Prefixes).get
+    var edges: Seq[DiEdge[Resource]] =
+      answers.collect { case (_, Seq(n1, n2)) => n1 ~> n2 }
+    val graph = Graph(edges: _*)
+
+    /* Close connection to RDFox */
+    RDFoxUtil.closeConnection(server, data)
+
+    (graph, nodemap)
+  }
+
+  def apply(axioms: List[OWLLogicalAxiom], datafiles: List[File]): Ontology =
+    new Ontology(axioms, datafiles)
+
+  def apply(ontology: OWLOntology, datafiles: List[File]): Ontology = {
+
+    /** TBox axioms */
+    var tbox: List[OWLLogicalAxiom] =
+      ontology
+        .tboxAxioms(Imports.INCLUDED)
+        .collect(Collectors.toList())
+        .collect { case a: OWLLogicalAxiom => a }
+
+    /** RBox axioms */
+    var rbox: List[OWLLogicalAxiom] =
+      ontology
+        .rboxAxioms(Imports.INCLUDED)
+        .collect(Collectors.toList())
+        .collect { case a: OWLLogicalAxiom => a }
+
+    /** ABox axioms
+      *
+      * @note this represents only the set of assertions contained in the
+      * ontology file. Data files specified in `datafiles` are directly
+      * imported in RDFox due to performance issues when trying to import
+      * large data files via OWLAPI.
+      */
+    var abox: List[OWLLogicalAxiom] =
+      ontology
+        .aboxAxioms(Imports.INCLUDED)
+        .collect(Collectors.toList())
+        .collect { case a: OWLLogicalAxiom => a }
+
+    Ontology(abox ::: tbox ::: rbox, datafiles)
+  }
+
+  def apply(ontofile: File, datafiles: List[File]): Ontology = {
+    val ontology = manager.loadOntologyFromOntologyDocument(ontofile)
+    Ontology(ontology, datafiles)
+  }
+
+}
+
+/** A wrapper for a generic OWL2 ontology
+  *
+  * @param axioms list of axioms (roughly) corresponding to the TBox.
+  * @param datafiles files containing ABox data.
+  */
+class Ontology(val axioms: List[OWLLogicalAxiom], val datafiles: List[File]) {
+
+  /** Extend OWLAxiom functionalities */
+  import uk.ac.ox.cs.rsacomb.implicits.RSAAxiom._
+
+  /** Simplify conversion between Java and Scala collections */
+  import uk.ac.ox.cs.rsacomb.implicits.JavaCollections._
+
+  println(s"Axioms: ${axioms.length}")
+
+  /** OWLOntology based on input axioms
+    *
+    * This is mainly used to instantiate a new reasoner to be used in
+    * the computation of unsafe roles.
+    */
+  protected val ontology: OWLOntology =
+    Ontology.manager.createOntology((axioms: List[OWLAxiom]).asJava)
+
+  /** OWLAPI internal reasoner for ontology */
+  protected val reasoner =
+    (new StructuralReasonerFactory()).createReasoner(ontology)
+
+  /** Unsafe roles in the ontology
+    *
+    * Unsafety conditions are the following:
+    *
+    * 1) For all roles r1 appearing in an axiom of type T5, r1 is unsafe
+    *    if there exists a role r2 (different from top) appearing in an
+    *    axiom of type T3 and r1 is a subproperty of the inverse of r2.
+    *
+    * 2) For all roles p1 appearing in an axiom of type T5, p1 is unsafe
+    *    if there exists a role p2 appearing in an axiom of type T4 and
+    *    p1 is a subproperty of either p2 or the inverse of p2.
+    */
+  lazy val unsafe: List[OWLObjectPropertyExpression] = {
+
+    /* Checking for unsafety condition (1) */
+    val unsafe1 = for {
+      axiom <- axioms
+      if axiom.isT5
+      role1 <- axiom.objectPropertyExpressionsInSignature
+      roleSuper = role1 +: reasoner.superObjectProperties(role1)
+      axiom <- axioms
+      if axiom.isT3 && !axiom.isT3top
+      role2 <- axiom.objectPropertyExpressionsInSignature
+      if roleSuper contains role2.getInverseProperty
+    } yield role1
+
+    /* Checking for unsafety condition (2) */
+    val unsafe2 = for {
+      axiom <- axioms
+      if axiom.isT5
+      role1 <- axiom.objectPropertyExpressionsInSignature
+      roleSuper = role1 +: reasoner.superObjectProperties(role1)
+      axiom <- axioms
+      if axiom.isT4
+      role2 <- axiom.objectPropertyExpressionsInSignature
+      if roleSuper.contains(role2) ||
+        roleSuper.contains(role2.getInverseProperty)
+    } yield role1
+
+    unsafe1 ++ unsafe2
+  }
+
+  /** Compute the dependency graph for the ontology */
+  lazy val dependencyGraph: Ontology.DependencyGraph =
+    Ontology.dependencyGraph(axioms, datafiles, this.unsafe)
+
+  /** RSA check */
+  lazy val isRSA: Boolean = ???
+
+  /** Normalize the ontology according to the given normalizer
+    *
+    * @param normalizer the normalization technique to be used.
+    * @return a new normalized [[Ontology]].
+    */
+  def normalize(normalizer: Normalizer): Ontology =
+    new Ontology(
+      axioms flatMap normalizer.normalize,
+      datafiles
+    )
+
+  /** Approximate the ontology according to the given approximation
+    * technique.
+    *
+    * @param approximation the approximation to be used on the ontology.
+    * @return the result of the approximation.
+    */
+  def approximate[T](approximation: Approximation[T]): T =
+    approximation.approximate(this)
+}