Is there a unique field that identifies a concept from others across all sources?
The id field within a source cannot be changed BUT it’s not unique across all other sources and I’d imagine this helps with flexibility.
The uuid field appears to be a numeric value (with no option of entering it in the app/api?). Does it uniquely identify a concept across the system?
Thank you.
Yes uuid is OCL generated uniq ID. It cannot be entered/edited from outside.
But uuid cannot be used in URLs to get concept info.
Hi @amoko, great question. And thanks @Sny for responding! I wrote this up yesterday but forgot to send it. 
What Sunny said is right, and I wanted to add one thing:
OCL’s External ID field (often stored as UUIDs which is separate the OCL’s uuid field) is often is intended to be unique within a non-OCL system e.g. OpenMRS. OpenMRS runs validations to make sure that there is only a single concept with the same External ID i.e. UUID. However, there’s no guarantee that the ID is truly unique if someone makes a copy of that concept in another source.
Thank you so much for the detailed response.