@Transient
	public String getLifetime(){
		StringBuilder builder = new StringBuilder();
		
		if (beginDocument != null && beginDocument != Document.FUTURE) {
			builder.append(lifetimeFormat.format(beginDocument.getDate()));
		}
		else {
			builder.append("unknown");
		}
		
		builder.append("-");
		
		if (endDocument != null && endDocument != Document.FUTURE) {
			builder.append(lifetimeFormat.format(endDocument.getDate()));
		}
		else{
			builder.append("unknown");	
		}
		
		return builder.toString();
	}