code: protected boolean semanticallyEquivalent(BioPAXElement element)
  	{
  		final bioSource bioSource = (bioSource) element;
  
  		return
  			(CELLTYPE != null ?
  				CELLTYPE.equals(bioSource.getCELLTYPE()) :
  				bioSource.getCELLTYPE() == null)
  				&&
  				(TAXON_XREF != null ?
  					TAXON_XREF.equals(bioSource.getTAXON_XREF()) :
  					bioSource.getTAXON_XREF() == null)
  				&&
  				(TISSUE != null ?
  					!TISSUE.equals(bioSource.getTISSUE()) :
  					bioSource.getTISSUE() != null);
  	}
docs: --------------------- Interface BioPAXElement ---------------------