Definitions for Entities that are Things

[mmccool]

Add two definitions:

• Device is a physical entity that has a network interface. Devices can be described by a Thing Description and are a kind of Thing.
• Service is a software entity that has a network interface. Services can be described by a Thing Description and are a kind of Thing.

The intention is that both Devices and Services, since they can be described by Thing Descriptions, are Things.

[mmccool]

Can also propose a definition for Virtual Thing: a kind of service that represents another Thing.

Examples are Digital Twins and Shadows. Shadows keep a copy of state of other Things. Digital Twins may do that but may also have the ability to predict future states or behaviour, and may also maintain a history of past state (suggest a list of additional functionalities for Twins that if an entity has at least one can be called a Twin).

Will not include these in this PR, just putting out there for discussion. (Actually, we did decide to deal with these too, and the are in the PR now)

[ashimura]

As I mentioned during the WoT Editors call yesterday on Feb. 15, it might make sense to look into the definitions and acronyms by oneM2M again:

• https://onem2m.org/using-onem2m/developers/basics
• https://onem2m.org/images/files/deliverables/TS-0011-Common_Terminology-V1_2_1.pdf

[k-toumura]

As a starting point for discussion, I've drawn a diagram of the Thing-related terms being discussed.

In this diagram, I've separated the Physical Device from the software that makes them network-accessible (Physical Things).

(The diagram is attached as SVG file, so please feel free to fetch, rewrite, and upload it for discussion.)

[mmccool]

Thanks for the diagram. Let's discuss next time we get a chance... but I'm thinking something even simpler, like a UML diagram showing subclass relationships among our definitions, would be helpful.

[mlagally]

This is a great diagram and unfortunately I just see it now after our architecture call.
We should include it in the architecture specification, need to find a good plave.