code: private static Map<String, Set<BioPAXElement>> collectEntityRefs(Collection<SIFInteraction> inters)
  	{
  		Map<String, Set<BioPAXElement>> map = new HashMap<String, Set<BioPAXElement>>();
  
  		for (SIFInteraction inter : inters)
  		{
  			if (!map.containsKey(inter.sourceID))
  				map.put(inter.sourceID, new HashSet<BioPAXElement>());
  			if (!map.containsKey(inter.targetID))
  				map.put(inter.targetID, new HashSet<BioPAXElement>());
  
  			map.get(inter.sourceID).addAll(inter.sourceERs);
  			map.get(inter.targetID).addAll(inter.targetERs);
  		}
  		return map;
  	}
docs: Collects the sources and targets in given interactions.
  @param inters binary interactions
  @return map from the primary id to the set of related source and target elements.