code: private OSchemaHelper oClass(String className, boolean abstractClass, String... superClasses)
  	{
  		lastClass = schema.getClass(className);
  		if(lastClass==null)
  		{
  			OClass[] superClassesArray = new OClass[superClasses.length];
  			for (int i = 0; i < superClasses.length; i++) {
  				String superClassName = superClasses[i];
  				superClassesArray[i] = schema.getClass(superClassName);
  			}
  			lastClass = abstractClass ? schema.createAbstractClass(className, superClassesArray) 
  									  : schema.createClass(className, superClassesArray);
  		} else {
  			boolean currentlyAbstract = lastClass.isAbstract();
  			if(currentlyAbstract!=abstractClass) lastClass.setAbstract(abstractClass);
  		}
  		lastProperty = null;
  		lastIndex = null;
  		return this;
  	}
docs: Create if required {@link OClass}
  @param className name of a class to create
  @param abstractClass is this class abstract
  @param superClasses list of superclasses
  @return this helper