- From: David Booth <david@dbooth.org>
- Date: Tue, 4 Dec 2018 15:52:19 -0500
- To: semantic-web <semantic-web@w3.org>, Aiden Hogan <aidhog@gmail.com>
- Cc: Henry Story <henry.story@bblfish.net>
On 12/4/18 3:30 PM, David Booth wrote: > On 12/3/18 8:29 AM, Henry Story wrote: > > . . . So what are the advantages of blank nodes > > pragmatically? They make a description local to the graph > > in which they appear and this locality is maintained > > across merges. The meaning of URI referenced resources can > > be completed by external information of course but the > > description ensures that no further links need to be taken > > into account when understanding the bnode's meaning. So it > > looks like it's ideal for things that need to be entirely > > defined by description. > > Interesting point! That means that blank nodes enjoy a > form of closed world assumption (CWA), in that there *cannot* > be any other triples asserted (directly) about a blank node, > other than the ones already in the document/graph/dataset > at hand. (Inference could add some though.) > > Of course, if we are dealing with implicit blank nodes -- the ones > generated by [] or () notation in Turtle -- then it's even more obvious > that the only property connections to/from that blank node are the ones > provided right there. > > This brings me to an interesting question. To rephrase, the "identity" > of a blank node object is determined entirely by the identities of its > connected nodes, because it is guaranteed to not have any other > connections. Therefore, a blank node labeling algorithm (or standard > Skolemization algorithm) only needs to take into account the subgraph of > that blank node's tightly connected neighbors. By "tightly connected" I > mean the subgraph that is connected only through consecutive blank > nodes. (I think this may be slightly different from the Concise Bounded > Description (CBD), because the CBD starts only with the *subject* of a > triple.) > https://www.w3.org/Submission/CBD/ > > Aiden (or someone else), is this correct? If so, this would be very > beneficial, because the labeling algorithm could then be guaranteed to > generate the *same* label (or Skolem URI) for the blank nodes in that > subgraph, regardless of any larger graph in which that subgraph appears. > This is very pertinent to n-ary relations, because it means that blank > nodes for the same n-ary relation, appearing in different RDF graphs, > could be automatically given the *same* label (or Skolem URI) -- even > without knowing a key for that object. Aiden, is this what such > canonicalization algorithms already do? P.S. this would also be very beneficial for the "diff" use case of RDF canonicalization, because it would help localize graph labeling differences. David Booth > > David Booth
Received on Tuesday, 4 December 2018 20:52:41 UTC