write a PR on rdf-concepts for the unstar mapping

[ghurlbot]

Opened by pchampin via IRC channel #rdf-star on irc.w3.org

Due: 2024-10-01 (Tuesday 1 October)

[pchampin]

This was discussed during the rdf-star meeting on 24 September 2024.

View the transcript

Un-star operation to support RDF Dataset Canonicalization?

gkellogg: we talk about "un-star" since long time
… we want to transform the representation in some form of other representation
… I assumed this will be standard reification.
… is the mechanism by which we transform triple terms simply reification triples?
… should we use different types and properties for reification triples?

<bengo> w3c/rdf-star-wg#114

<gb> Issue 114 Un-star operation to support RDF Dataset Canonicalization? (by niklasl) [needs discussion] [discuss-f2f]

pchampin: from the CWG: we defined RDF-Star semantics on top of the standard RDF semantics
… we are using the same term "un-star" for a totally different purpose now
… many people asked why do you not just singleton named graphs.
… I inteded to write something and share it in advance but didn't manage to.
… do we want to have the "un-star" mapping to be lossless?
… I have a simpler version but it's not 100% lossless

<Zakim> gkellogg, you wanted to discuss conflation with reifiers and graph names

gkellogg: the issue is that we might create something that inserts triple in an existing named graph

pchampin: using reifiers as graph names would definitely create a number of issues. I would rather go for encoding each triple term into a blanknode made singleton named graph
… we encode the triple term into a singleton named graph that is a blank node
… we also add another graph that says "this blank node is a triple term"
… and any other blank node that is a triple term.

pchampin: I try to keep the un-star mapping as liberal as possible.
… if there is no triple term in an existing dataset this should work. but if you have already an un-star set in it, it becomes an edge-case
… with that we could convert every RDF-Star 1.2 into RDF 1.1 "classic"

<Zakim> AndyS, you wanted to ask about scope of the solution

AndyS: we might want to convert an RDF 1.1 graph with reification into a RDF 1.2 graph.
… what pchampin talked about, it got complicated once you said you want to put a dataset into a dataset that already contains a graph that has reification
… we might simplify that by saing it's two datasets and it becomes a merge operation

gtw: we should do that per triple-term. it's natural thing to look at what that looks like per reifier.

tl: Dydra already implements RDF-Star with named graphs. there is some experience
… they are happy to share the experience.
… The mapping to standard triples with the RDF reification vocab would be useful too and I would like to have it lossless

<Zakim> bengo, you wanted to ask if unstar to graph and unstar to dataset are both useful to standardize for different reasons

bengo: it would be useful to un-star to triples or graphs for different reasons.

pchampin: to respond to AndyS about staring standard reification: that is for me a totally different problem, it was not my intention in that proposal
… I had two goals: Canonicalization & flattening

gkellogg: regarding the notion to create named graphs per reifiers.
… querying would become much more difficult.

niklasl: it's important to un-star to RDF "classic" for a number of reasons
… for example to be able to add it to an existing graph store as soon as possible
… the problem is union graphs that many stores do.
… I believe using classic reification properties is frugal.

tl: we had an experiment with nested named graphs. the problem is that we have to extend SPARQL to query that. triple terms are much more powerful in that respect.
… it wouldn't be that easy with just named graphs. and also other reasons. things get tricky on SPARQL level

ACTION: pchampin to write a PR on rdf-concepts for the unstar mapping

<gb> Created action #129

ora: the question is how much effort do we want to put into edge cases that might not occur anyway

pchampin: I will write a pull-request with some examples

ora: this will go back into the backlog

pchampin: let's scan the backlog to prepare for Thursday as well

ora: good idea

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[afs]

See also #114

[niklasl]

Also related: w3c/rdf-semantics#49; specifically the tentative terms used. Those terms rely on terms to be defined through the alternative baseline.