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"from" and "to" codes (or expressions of codes)
Represented as an association with qualifiers for other semantically important information
If target is an expression, represented as an “association to data”
Have “default preferred name” in the event that a "from"/"to" code cannot be resolved in a loaded coding scheme
"map rank" may be a standard part of the model.  If so, values should be normalized, so that 1 always means "best" and increasing numbers represent lowering quality (exactly how much lower and why is map set dependent).

1.4 Mapping attributes

Any information about a mapping than what directly fits the “association” object model will be rendered as attributes. Hopefully these attributes will have standard names across different types of map set loader. In other words – we can define the semantics of mapping association qualifiers so that particular ones are used to always represent the same aspect of some kind of mapping semantics.

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