Use, but don't store, foaf:primaryTopic on RDF Create

[catch-point]

If the POST'd RDF document for creation includes a primaryTopic use that as the created URI (not the first subject).

If request includes Slug header, use that as base-uri, otherwise parse with a generated base-uri. If document include a foaf:primaryTopic relationship from the base-uri, use the first target URI as the created URI. Don't realize foaf:primaryTopic relationships with the base-uri as the subject.

In the created response, include a describedby response Link header to the created URI's describe URL.

Some examples might include:

use generated base-uri, which will determine the file URI

POST /folder/?describe
<> rdfs:label "file".

use slug as base-uri for created URI

POST /folder/?describe
Slug: file
<> rdfs:label "file".

use generated base-uri, whose local value doesn't matter

POST /folder/?describe
<file> rdfs:label "file".

use generated base-uri, whose local value doesn't matter

POST /folder/?describe
<> foaf:primaryTopic <file> .
<file> rdfs:label "file".

use slug as base-uri, whose value doesn't matter

POST /folder/?describe
Slug: whatever
<> foaf:primaryTopic <file> .
<file> rdfs:label "file".

As per 4.2.1.5, 5.2.3.7, 5.2.3.10, and 5.2.3.12 http://www.w3.org/TR/ldp/ to use these client hints.