Lightweight semaphore mechanism #3
Description
@timbl suggested in his RWW Design Issue that DELETE INSERT WHERE queries could be used for a semaphore mechanism, so that if the DELETE part fails, a conflict flag should be raised.
I think the mechanism can be illustrated with simpler DELETE DATA/INSERT DATA queries, so here's my description:
Say that client 1 goes:
DELETE DATA { <foo> <baz> "Dahut" } ;
INSERT DATA { <foo> <baz> "Bar" }independently, client 2 goes
DELETE DATA { <foo> <baz> "Dahut" } ;
INSERT DATA { <foo> <baz> "Foobar" }before the first client as finished. In that case, the Solid implementation
would return a 409 Conflict to the second client.
There are a few problems, as noted in solid/solid-spec#193 it is a willful violation of the SPARQL 1.1 specification, which says:
Deleting triples that are not present, or from a graph that is not present will have no effect and will result in success.
Moreover, reporting a success or failure status to DELETE queries are problematic from a confidentiality perspective, as is the topic of #2 .