code: package it.unibz.inf.ontop.model.term.functionsymbol.db.impl;
  
  import com.google.common.collect.ImmutableList;
  import it.unibz.inf.ontop.model.term.ImmutableTerm;
  import it.unibz.inf.ontop.model.term.TermFactory;
  import it.unibz.inf.ontop.model.term.functionsymbol.db.DBFunctionSymbol;
  import it.unibz.inf.ontop.model.term.functionsymbol.db.DBFunctionSymbolSerializer;
  import it.unibz.inf.ontop.model.term.functionsymbol.impl.FunctionSymbolImpl;
  import it.unibz.inf.ontop.model.type.DBTermType;
  import it.unibz.inf.ontop.model.type.TermType;
  import it.unibz.inf.ontop.model.type.TermTypeInference;
  import it.unibz.inf.ontop.utils.ImmutableCollectors;
  
  import javax.annotation.Nonnull;
  import java.util.Optional;
  import java.util.function.Function;
  import java.util.stream.Collectors;
  import java.util.stream.IntStream;
  
  /**
   * Function symbols of which we don't know the return type.
   *
   * By default, it is treated as non-injective and non-postprocessable.
   * They also may not reject NULLs and produce NULLs without having NULLs as input.
   *
   * This class is typically used for not recognized DB functions (e.g. when parsing the mapping)
   *
   * IMPORTANT ASSUMPTION (could be possibly violated as the function symbol is not recognized)
   *   1. The function symbol is DETERMINISTIC
   *
   */
  public class DefaultUntypedDBFunctionSymbol extends FunctionSymbolImpl implements DBFunctionSymbol {
  
      private final DBFunctionSymbolSerializer serializer;
  
      protected DefaultUntypedDBFunctionSymbol(@Nonnull String nameInDialect, int arity, DBTermType rootDBTermType) {
          super(nameInDialect + arity, IntStream.range(0, arity)
                  .mapToObj(i -> (TermType) rootDBTermType)
                  .collect(ImmutableCollectors.toList()));
          this.serializer = Serializers.getRegularSerializer(nameInDialect);
      }
  
      @Override
      public boolean isAlwaysInjectiveInTheAbsenceOfNonInjectiveFunctionalTerms() {
          return false;
      }
  
      @Override
      public final Optional<TermTypeInference> inferType(ImmutableList<? extends ImmutableTerm> terms) {
          return Optional.empty();
      }
  
      @Override
      protected boolean mayReturnNullWithoutNullArguments() {
          return true;
      }
  
      @Override
      public boolean canBePostProcessed(ImmutableList<? extends ImmutableTerm> arguments) {
          return false;
      }
  
      @Override
      public String getNativeDBString(ImmutableList<? extends ImmutableTerm> terms,
                                      Function<ImmutableTerm, String> termConverter, TermFactory termFactory) {
          return serializer.getNativeDBString(terms, termConverter, termFactory);
      }
  
      @Override
      protected boolean tolerateNulls() {
          return true;
      }
  
      @Override
      public boolean isPreferringToBePostProcessedOverBeingBlocked() {
          return false;
      }
  }
  