code: private int getLiteralId(String literal) throws PersistenceBrokerException
      {
          ////logger.debug("lookup: " + literal);
          try
          {
              return tags.getIdByTag(literal);
          }
          catch (NullPointerException t)
          {
              throw new MetadataException("unknown literal: '" + literal + "'",t);
          }
  
      }
docs: returns the XmlCapable id associated with the literal.
  OJB maintains a RepositoryTags table that provides
  a mapping from xml-tags to XmlCapable ids.
  
  @param literal the literal to lookup
  @return the int value representing the XmlCapable
  
  @throws MetadataException if no literal was found in tags mapping