Do we need to support core mapping identifiers?

[matentzn]

In a SSSOM TSV, and individual row corresponds to a metadata record about a mapping, not a core mapping.

The core mapping is comprised of:

1. subject_id
2. predicate_id
3. object_id
4. predicate_modifier

To be able to identify a core mapping in a semantic web context and talk about it, people are asking how the URI representing those mappings should be captured.

Here we need to discuss the why: What is your use case for needing to talk about the core mapping in isolation of its metadata / justifications?

[joeflack4]

FYI I'm partial to the term "mapping quad" for this.
We've been discussing the merits and demerits of this in #359, but for the record I'm ambivalent / opposed unless a strong use case emerges or users start asking for it.