Update Discovery Requirements

[mmccool]

Update requirements in https://github.com/w3c/wot-usecases/blob/main/REQUIREMENTS/discovery.md - can be before or after merging into the UC document as proposed in w3c/wot#1110.

Possible new requirements:

• Supported by Constrained Devices
  • Small devices with limited memory and processing should be able to participate in WoT Discovery as both providers and consumers
• Integration with Existing Discovery Mechanisms
  • E.g. MQTT discovery, OPC UA discovery

For other possible requirements we should look at the existing use cases.

[AndreaCimminoArriaga]

I think it could be interesting to have a feature to automatically discover what is deployed in the local network, thinking in SmartHome alike use cases. On the other hand, thanks to the SPARQL federation feature a distributed discovery capability would be nice

[mmccool]

See also #231 - will update in UC&R doc, at which point we should delete/archive the MD file to avoid duplication and confusion.

[mmccool]

@AndreaCimminoArriaga that seems like a use case, that will in turn drive a requirement. Can you create a use case for consideration by the Use Case TF? We do need something to motivate "local" discovery (which we can do already, with a combination of mDNS and .well-known self-description TDs, for instance - harder for "brownfield" devices). However, note in our current model directories do not actively search for things, they only accept registrations. We would need to suggest a new feature to actively look for things and register them - but to be clear, "active search" for unknown things would be a "new" service, and not covered by the current spec. But a clear use case for this would help organize the discussion about whether this is a requirement we want to satisfy.