I've had an idea for a while for something that I'd refer to as brother and sister service checks. There are occasions where I would like to monitor a particular 'service' in more than one way, but architect it in such a way where I only receive one notification. My best example would be a dry contact sensor via SNMP. One method is to receive an SNMP trap via SNMPTT. The other is to actively check the OID of the dry contact sensor. I like the idea of processing the trap because it is instantaneous, but it is prone to failure. So I'd back it up with a traditional check_snmp service check. I'd like to be able to define the two checks as related so that if one changes state and generates a notification, the other won't do the same. I don't see this as a dependency ... but perhaps there is a way to use the dependency logic to accomplish my goal?
A similar example would be watching a webserver via check_tcp and via check_http. Generally, a dependency relationship would probably work here but the idea of a brother/sister check could present some interesting opportunities.