Four Essential Technical Criteria
1. Concept Orientation: Elements of the terminology are coded concepts, with possible multiple synonymous text representations, and hierarchical or definitional relationships to other coded concepts.
2. Concept Permanence: The meaning of each code concept in a terminology remains forever unchanged. If the definition of a concept needs to be changed or refined, a new code concept is introduced. No retired codes are deleted or re-used.
3. Non-Ambiguity: Each coded concept in the terminology has a unique meaning. 4. Explicit Version Identifiers: Each version of the terminology is designated with a unique
identifier, such that parties exchanging data can readily determine if they are using the same set of terms.