Use biolink Named Thing as root node

[wdduncan]

The current root node is Entity. I think it would be advantageous to use Biolinks Named Thing as the root.

This allows for easier integration with Biolink and consistency across projects using LinkML (e.g., NMDC's Named Thing.

[bfurner]

There appears to be some inconsistencies here. It looks like the Biolink model has 'Entity' as it's root element with 'NamedThing' as a child: https://biolink.github.io/biolink-model/docs/Entity.html. NMDC, on the other hand, does have a root entity of 'NamedThing'

@mbrush do you have thoughts on Entity vs NamedThing?

[wdduncan]

@bfurner Ah yes ... you are right Biolink does have an entity class. I like the clean separation between named things and associations. This might benefit the ccdh model.