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  package org.apache.cayenne.ejbql;
  
  /**
   * An abstract EJBQL expression interface.
   * 
   * @since 3.0
   */
  public interface EJBQLExpression {
  
      /**
       * Accepts a visitor, calling appropriate visitor method. If the visitor method
       * returns true, visits all children, otherwise stops.
       */
      void visit(EJBQLExpressionVisitor visitor);
  
      /**
       * Returns a number of child operands of this expression node.
       */
      int getChildrenCount();
  
      /**
       * Returns a child expression node at the specified index.
       */
      EJBQLExpression getChild(int index);
  
      /**
       * Returns a text property of the node.
       */
      String getText();
  
      /**
       * Returns an optional boolean flag that negates the value of the expression.
       */
      boolean isNegated();
  }
  