public void unloadGroup(CogaenId groupId) {
		List<ResourceHandle> group = this.groups.get(groupId);
		if (group == null) {
			throw new RuntimeException("unonkown resource group " + groupId);
		}
		
		this.logger.logInfo(LOGGING_SOURCE, "unloading resource group " + groupId);
		for (ResourceHandle handle : group) {
			if (handle.isLoaded()) {
				try {
					handle.unload(getCore());
					this.logger.logDebug(LOGGING_SOURCE, "unloaded resource: " + this.invResourceMap.get(handle));					
				} catch (ResourceException e) {
					this.logger.logWarning(LOGGING_SOURCE, "unable to unload resource: " + e.getMessage());					
				}
			}
		}
	}