ComponentAccess lookup(Object cmd) {
		if (cmd == null) {
			throw new ComponentException("null component.");
		}
		if (cmd == ca.getComponent()) {
			throw new ComponentException("Cannot add the compound to itself "
					+ cmd.toString());
		}
		ComponentAccess w = oMap.get(cmd);
		if (w == null) {
			oMap.put(cmd, w = new ComponentAccess(cmd, ens));
		}
		return w;
	}