code: package it.unibz.inf.ontop.model.term.functionsymbol.db.impl;
  
  import com.google.common.collect.ImmutableList;
  import it.unibz.inf.ontop.iq.node.VariableNullability;
  import it.unibz.inf.ontop.model.term.*;
  import it.unibz.inf.ontop.model.type.DBTermType;
  
  /**
   * IF cond THEN v1 ELSE v2
   *
   * TODO: simplify strict equalities
   *
   */
  public abstract class AbstractDBIfThenElseFunctionSymbol extends AbstractDBIfThenFunctionSymbol {
  
      protected AbstractDBIfThenElseFunctionSymbol(DBTermType dbBooleanType, DBTermType rootDBTermType) {
          super("IF_THEN_ELSE", 3, dbBooleanType, rootDBTermType, false);
      }
  
      @Override
      protected ImmutableTerm extractDefaultValue(ImmutableList<? extends ImmutableTerm> terms, TermFactory termFactory) {
          return terms.get(2);
      }
  
      @Override
      public ImmutableTerm simplify(ImmutableList<? extends ImmutableTerm> terms,
                                    TermFactory termFactory, VariableNullability variableNullability) {
          ImmutableTerm defaultValue = extractDefaultValue(terms, termFactory);
  
          if (defaultValue.equals(termFactory.getNullConstant()))
              return termFactory.getIfElseNull((ImmutableExpression) terms.get(0), terms.get(1))
                      .simplify(variableNullability);
  
          if (terms.get(1).equals(defaultValue))
              return defaultValue;
  
          return super.simplify(terms, termFactory, variableNullability);
      }
  
      /**
       * Only looks if the second and third argument are guaranteed to be post-processed or not
       * since the first argument (the condition expression) will always be evaluated.
       */
      @Override
      public boolean canBePostProcessed(ImmutableList<? extends ImmutableTerm> arguments) {
          return extractSubFunctionalTerms(arguments.subList(1, 3))
                  .allMatch(ImmutableFunctionalTerm::canBePostProcessed);
      }
  }
  