ISSUE-21: Can Node-IDs be shared between parts of a quad/multigraph format?

Shared Node-IDs

Can Node-IDs be shared between parts of a quad/multigraph format?

State:
CLOSED
Product:
RDF Graphs
Raised by:
Sandro Hawke
Opened on:
2011-04-01
Description:
Can we serialize in a multigraph format the state of a quadstore that happens to have blank nodes shared between graphs?

Alternatively:

Given N-Quads:

_x: <http://example.org/p1> 1 <http://example.org/id1> .
_x: <http://example.org/p1> 2 <http://example.org/id2> .

if id1 and id2 were merged, would the resulting graph have three nodes or four?

Use cases for allowing them to be shared include:

- SPARQL default graph being the merge of the named graphs
- proof trees, details of inference over graphs
- highlighting/annotating subgraphs, for provenance
Related Actions Items:
No related actions
Related emails:
  1. Re: Moving forward on ISSUE-21 (from guus.schreiber@vu.nl on 2012-09-10)
  2. Moving forward on ISSUE-21 (was: Re: Re3 : Draft for a 'minimal dataset semantics') (from richard@cyganiak.de on 2012-09-07)
  3. Re: Scope of blank nodes in RDF (from sandro@w3.org on 2012-09-06)
  4. Re: Scope of blank nodes in RDF (from sandro@w3.org on 2012-09-06)
  5. Re: Oracle Using TriG? (from david@3roundstones.com on 2012-09-05)
  6. Re: Oracle Using TriG? (from alan.wu@oracle.com on 2012-09-05)
  7. Oracle Using TriG? (from david@3roundstones.com on 2012-09-05)
  8. Re: shared bnodes (Skolems, SPARQL) (from steve.harris@garlik.com on 2012-09-01)
  9. Re: shared bnodes (Skolems, SPARQL) (from sandro@w3.org on 2012-08-31)
  10. Re: shared bnodes (Skolems, SPARQL) (from andy.seaborne@epimorphics.com on 2012-08-31)
  11. Re: shared bnodes (Skolems, SPARQL) (from steve.harris@garlik.com on 2012-08-31)
  12. RE: shared bnodes (Skolems, SPARQL) (from markus.lanthaler@gmx.net on 2012-08-30)
  13. Re: shared bnodes (Skolems, SPARQL) (from andy.seaborne@epimorphics.com on 2012-08-29)
  14. Re: shared bnodes (Skolems, SPARQL) (from sandro@w3.org on 2012-08-29)
  15. Re: [ALL] agenda 11 May telecon (from sandro@w3.org on 2011-05-11)
  16. Re: RDF-ISSUE-21 (Shared Node-IDs): Can Node-IDs be shared between parts of a quad/multigraph format? [RDF Graphs] (from david.wood@talis.com on 2011-04-01)
  17. Re: Turtle support for Multiple Graphs, suggestion (from sandro@w3.org on 2011-04-01)
  18. RDF-ISSUE-21 (Shared Node-IDs): Can Node-IDs be shared between parts of a quad/multigraph format? [RDF Graphs] (from sysbot+tracker@w3.org on 2011-04-01)

Related notes:

I've always understood the scope of blank nodes to be the enclosing graph, so the merge of those two graphs will have two different subjects.

Consider two ntriples files each containing one of those statements, understood as two separate graphs. They are then collated into a nquads file as represented in the example. Merging the two originals would not merge the two _x:. So merging the collated version shouid give the same result.

I realise this is seriously inconvenient for the use cases described but perhaps an answer can be found in the skolem proposals. That would fix the scoping problem and allow merging the _x: or not depending on the author's intention.

William Waites, 1 Apr 2011, 22:58:40

The RDF documents were written before quad stores were contemplated, so the answer is not completely clear. It depends upon how one construes the graph 'label' in the last quad position. If these are understood as analogous to graph names, so that each set of triples (extracted from quads) with the same identifier is a distinct RDF graph, then the bnode IDs should be understood to be unique to those graphs, so this example would have triples with distinct subjects: four nodes, with two nodes in each graph. If, on the other hand, the fourth quad field is understood as identifying a subgraph of a single large graph, then this large graph would be the appropriate scope for the bnodeIDs, and the example would be three nodes in a single graph.

-Pat Hayes

Patrick Hayes, 18 May 2011, 14:28:54

http://www.w3.org/2012/09/12-rdf-wg-irc#T16-06-28

<sandro> RESOLVED: Close ISSUE-21 saying Yes, Node IDs are document scope in the multi-graph syntax (TriG, etc)

Sandro Hawke, 12 Sep 2012, 16:06:46

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