code: package it.unibz.inf.ontop.model.term.functionsymbol.db.impl;
  
  import com.google.common.collect.ImmutableList;
  import it.unibz.inf.ontop.model.term.ImmutableExpression;
  import it.unibz.inf.ontop.model.term.ImmutableTerm;
  import it.unibz.inf.ontop.model.term.TermFactory;
  import it.unibz.inf.ontop.model.type.DBTermType;
  
  import java.util.function.Function;
  
  
  public abstract class AbstractDBNonStrictEqOperator extends DBBooleanFunctionSymbolImpl {
  
      private static final String TEMPLATE = "(%s = %s)";
  
      protected AbstractDBNonStrictEqOperator(String functionSymbolName, DBTermType rootDBTermType,
                                              DBTermType dbBoolean) {
          super(functionSymbolName, ImmutableList.of(rootDBTermType, rootDBTermType), dbBoolean);
      }
  
      /**
       * Can be overridden
       */
      @Override
      public String getNativeDBString(ImmutableList<? extends ImmutableTerm> terms,
                                      Function<ImmutableTerm, String> termConverter, TermFactory termFactory) {
          return String.format(TEMPLATE, termConverter.apply(terms.get(0)), termConverter.apply(terms.get(1)));
      }
  
      @Override
      protected boolean tolerateNulls() {
          return false;
      }
  
      @Override
      public boolean isAlwaysInjectiveInTheAbsenceOfNonInjectiveFunctionalTerms() {
          return false;
      }
  
      /**
       * TODO: stop blocking
       */
      @Override
      public boolean blocksNegation() {
          return true;
      }
  
      @Override
      public ImmutableExpression negate(ImmutableList<? extends ImmutableTerm> subTerms, TermFactory termFactory) {
          throw new UnsupportedOperationException();
      }
  }
  