code: public void convertToOWL(Model model, OutputStream outputStream)
  	{
  		initializeExporter(model);
  
  		try
  		{
  			Writer out = new BufferedWriter(new OutputStreamWriter(outputStream, "UTF-8"));
  			writeObjects(out, model);
  			out.close();
  		}
  		catch (IOException e)
  		{
  			throw new BioPaxIOException("Cannot convert to OWL!", e);
  		}
  	}
docs: Converts a model into BioPAX (OWL) format, and writes it into
  the outputStream. Saved data can be then read via {@link BioPAXIOHandler}
  interface (e.g., {@link SimpleIOHandler}).
  
  Note: When the model is incomplete (i.e., contains elements that refer externals,
  dangling BioPAX elements) and is exported by this method, it works; however one
  will find corresponding object properties set to NULL later,
  after converting such data back to Model.
  
  Note: if the model is very very large, and the output stream is a byte array stream,
  then you can eventually get OutOfMemoryError "Requested array size exceeds VM limit"
  (max. array size is 2Gb)
  
  @param model model to be converted into OWL format
  @param outputStream output stream into which the output will be written
  @throws BioPaxIOException in case of I/O problems