- From: Dave Reynolds <der@hplb.hpl.hp.com>
- Date: Thu, 09 Jan 2003 11:52:05 +0000
- To: jena-dev@yahoogroups.com
- CC: www-rdf-interest@w3.org, Bob MacGregor <macgregor@isi.edu>
Bob MacGregor wrote: > > A very nice summary of the statements v. stating issue is in > > http://ilrt.org/discovery/2000/11/statements > > Near the end, three positions are layed out: > (1) 'reified statements are statings' > (2) 'statements are resources' > (3) 'change the model' (not a very self-explanatory label) > > I personally don't endorse the first interpretation, but I assume that > Seth does (see below). Thus, for him, quads make sense. I prefer that there > be a one-to-one correspondence between statements and > their reified counterparts. As I pointed out in my earlier message, the RDF core working group has endorsed position (1) that reified statements are statings. Personally, I agree with you that a 1-1 correspondence between statements and their reifications would be better but that is not the decision and so is not the proposed standard. You may wish to raise this on rdf-comments. > Jena's "shortcut" reification would seem to implicitly require a > one-to-one correspondence between statements and their > shortcut reifications (the mapping being the identity function). Correct. The Jena "shortcut" was based on a reading of the original M&S which we interpreted as endorsing this 1-1 correspondence. Now that the working group has "clarified" this, Jena2 will need to provide a slighly different version of the shortcut in which, for example, each statement may be associated with several "reifications". As you say, there is nothing to stop an application imposing additional constraints to ensure that in fact there is only ever one reification for each statement. > A part of my original use case question then becomes, how > efficiently can we implement these constraints using a triple > store API? For example, if a retrieval returns a statement > <a,b,c>, does it take a second query to determine if there > exists an X representing its reification (i.e., such that the triples > <X, subject, a> <X, predicate, b> <X, object, c> exist)? > It would be nice if the API gave us a fast way to acquire > X (if it exists), given a statement <a, b, c>. In an earlier > e-mail, I was wishing for a resource associable with > a shortcut reification. The X above can be that resource. I believe the proposed Jena2 reification API will, in principle, make it possible to efficiently determine if X exists so long as X is created in the first place using the modified shortcut. How efficient this is in practice will depend on the Model implementations. Had the working group not decided that reifications are statings then the current Jena RDB layout could have been reused in Jena2 and no additional queries would be required to find X. Given that the WG *has* made the decision the way it has, I presently have no idea how to implement a reification API efficiently in an RDB system. Dave
Received on Thursday, 9 January 2003 06:55:51 UTC