Value compaction seems to do a lot of unnecessary work

[daenney]

While I was implementing value compaction as per https://www.w3.org/TR/json-ld11-api/#value-compaction there seems to be some unnecessary work being performed.

Steps 2 and 3 are unnecessary, the inverse context is never used during value compaction. I assume this is a left-over from a previous draft of the spec?

Compact value is only ever called once during Compaction, in step 7:

If element has an @value or @id entry and the result of using the Value Compaction algorithm, passing active context, active property, and element as value is a scalar, or the term definition for active property has a type mapping of @json, return that result.

With the exception of the @json entry, the result from value compaction is always discarded if it's not a scalar. This would suggest that every step in Value Compaction where we return anything other than a scalar is not necessary. For a value that's @json, we don't want to perform IRI compaction of the keys as far as I understand it, which would also make step 11 in value compaction unnecessary. I might be wrong about this part. Since we only ever care for the scalar return, creating the copy of result in step 1 isn't necessary either.

It seems like we can simplify things by:

• In Compaction step 7:
  • First check if the type mapping is @json and return value without going through Value Compaction.
  • Then do the value compaction and return it if it's not null.
• Update the Value Compaction as follows:
  • Drop 1), 2), 3).
  • In step 8) keep the branch but do nothing.
  • Drop 11).
  • Update 12) to return null

These changes seem to work in my own processor without it causing anything in the compaction test suite to fail.

[gkellogg]

Steps 2 and 3 are unnecessary, the inverse context is never used during value compaction. I assume this is a left-over from a previous draft of the spec?

Likely, as the inverse context is indeed not used in value compaction. It's used in term selection, which then provides the active property to this algorithm.