Re: Named graphs etc

On Mar 11, 2004, at 01:31, ext Pat Hayes wrote:

>
> Ok, after more thinking.
>
> Clearly some sort of vocabulary solution would be the least painful 
> route to take, along the lines Jeremy suggests.  We have to face up to 
> the complications it introduces, though.  For example, what if an 
> agent wants to change their mind about G, but there's an assertion out 
> there that says that they are asserting G?

If they owned G, and the statement about asserting G was in G, then 
they'd just change or remove G.

> What's to stop a malicious publication of assertion that A asserts P 
> by some other agent B?

Because we only trust authoritative and authenticated statements about 
assertion.

If A is not the authority asserting P, per the statements in P, then we 
have cause
to conclude that A does not (necessarily) assert P.

> What if A asserts G  but then B says that G is deprecated?

This seems like a separate issue. It may very well be that for a given 
purpose
G is deprecated, and in that application area, we may trust B about 
such things,
but that doesn't affect whether G is asserted or authentic or who the 
authority
asserting G is.

> I think that we have to assume that there is a clear notion of the 
> agent-thing doing the asserting, and that any asserted graph has an 
> identifiable 'owner' who is the agent asserting it. I'm not sure how 
> we can guarantee that this is always possible, so I'll leave that on 
> the table as an issue.

I'd like to preserve a distinction between 'publisher/owner' and 
'agent'. It can
be that an agent can be a publisher of a graph, but I think there is a 
difference
between the 'publisher/owner' stating that a graph is asserted and some 
other
'agent' stating that the graph is asserted.

I actually do not think that it should be possible for anyone but the 
owner
to assert a graph (even though agents may make whatever statements they
like about the graph otherwise).

>
> How to do it, is the question. It can't be done simply by tweaking 
> truth-conditions (my previous gripe), so OK, we do it some other way. 
> It will be a rather unusual semantic extension, but still a semantic 
> extension.
>
> Lets hypothesize a class of 'RDF agents'. We don't need to say what 
> they are exactly (RFC 2396 doesn't say what a 'resource' is exactly) 
> but we suppose that they are resources which can perform 'web acts' 
> with respect to RDF graphs. Web acts are 'speech acts on the Web': 
> they include minimally
>
> asserting
> quoting
>
> and likely others not yet specified. Every assertion is made by an 
> agent. Given any record of an assertion, we have to be able to figure 
> out the agent of the assertion.

If we replace 'agent' with 'publisher' or 'authority', then I'm OK so 
far.

I don't, though, think that any agent other than the publisher/authority
can affect the assertiveness of a graph.

An agent can refer to a graph and make statements about that graph 
without
any relation to whether the graph is or is not asserted. Thus, an agent
could refer to a graph that is stated to be non-asserted (quoted) by
the graph authority as the hypothetical basis for some conclusion, yet
such a reference would not assert that unasserted graph (even if the
conclusion could not be reached without asserting it).

>
> Now, how does this relate to triples in graphs?? One view (1) (the one 
> I've been using, implicitly) is that a web act is somehow connected 
> with the publication of a graph: that the act happens when you hit the 
> 'upload' button and something gets written on your web server.  On 
> this view, a triple in a graph would at best be a kind of noting or 
> recording or a statement ABOUT the act, and the asserting agent is the 
> owner of the web resource where the (original) graph is located.  
> Another view (2), which I think Patrick is using, is that the 'act' is 
> performed by the graph itself: that to assert *is* to have a triple of 
> a certain kind in a graph.  He wants to be sure that graphs can only 
> assert themselves in this authoritative way, which makes sense on this 
> view. Also, on this view, as long as asserting triples can be firmly 
> anchored in named graphs, the locating-the-asserter problem is solved.
>
> However, I don't see how we can firmly locate triples in graphs in 
> this way, because how can we possibly legislate against people copying 
> triples from one graph to another?

Because the statements qualifying one graph are irrelevant to any other 
graph!

If some graph A contains the statement

    :A trix:asserted "true"^^xsd:boolean .

and graph A is merged into graph B, which has no
assertion statements -- that does *not* result in graph
B being asserted, because there would be no statement

    :B trix:asserted "true"^^xsd:boolean .

in graph B.


> And this mixes up several things, such as the propositional nature of 
> RDF and the distinction between a graph and a document containing the 
> graph, that seem to be fundamental; and it muddies up RDF with things 
> that look like locatives or indexicals ('this' or 'here') .

Please look at my recent discussions of these issues. You are presuming
the use of a "thisGraph" mechanism, which I've abandoned, as well as 
perhaps
presuming that somehow the RDF and/or OWL MTs have to deal with the
special semantics required, which I think they don't.

I think you will find my latest proposal, which outlines the two
phases of interpretation.

>
> So let me revert to the idea of a graph being a description of 
> something, and ask what it would be describing in this case. We could 
> say that a triple
>
> ex:agent rdfx:asserts ex:graph1
>
> is true when the 'state of the Web' is such that ex:agent is indeed 
> asserting, or has asserted and has not yet un-asserted, that graph. So 
> this can come to be true and false depending on the state of the Web, 
> which gives a model theorist nightmares but is something we have to 
> face up to.

Blech...

(tried for a more meaningful comment, but that's the best I came up 
with ;-)


>
> OK so far, but this still only has the graph describing - reporting on 
> - some event of asserting, rather than actually making anything 
> happen. So we need a kind of web act rule (compare Grice's rules of 
> conversational implicature :-) which says that if an agent publishes a 
> graph which describes a web act by that very agent, then the act is 
> deemed to have been done by that publication. That is, you cannot tell 
> RDF lies about your own web acts. (Cannot as in 'its impossible' not 
> as in 'its naughty')  Just like in English (actually, more like in 
> civilized English-speaking society) you cannot say "I promise..." 
> without actually promising.

You could be crossing your fingers....   ;-)


> I take it that this is what Jeremy meant about English doing the 
> speech acts. However, if you say "He promises..." then unless you are 
> empowered by him to to speak for him, eg by a power of attorney, then 
> nobody has promised anything: which is why we need the link between 
> the agent responsible for the triple, and the agent referred to by the 
> triple. The weakness of this whole story is then how to establish that 
> link between a triple and the agent responsible for it, so people can 
> tell genuine assertings from mere descriptions of assertings. I don't 
> have any good answer to that, but maybe we don't need to give a good 
> answer to it, if we state the issue clearly. (Is there a good answer 
> to the question "Who owns a web resource?")

Yes. Insofar as graphs are concerned. And that's provide for using the 
intra-graph vocabulary.

A given graph contains statements qualifying that graph regarding
assertiveness, authority, etc. and includes a signature for
authenticating/validating the graph to be sure about who said
what.

The who in "who owns this graph" is the authority specified in the
graph. And the assertiveness of the graph is specified also in the
graph. And trust of the statements asserted by that graph is based
on the authenticated authority of the graph.

Seems pretty simple to me (but then I tend to be a bit simple minded, 
eh ;-)

>
> This story could be applied to either (1) or (2) above, but if with 
> (1) there is no particular need to have the assertion be an assertion 
> of the graph it is in. What matters is that it is an assertion BY the 
> agent it says it is by.

But how do you *know* if the assertion is by the agent it says it is 
by? By another graph?!

> Its the domain rather than the range of rdfx:asserts that needs to be 
> anchored in some kind of checkable reality.
>
> One problem seems to me to be, who is responsible for stating a 
> general Gricean 'web act rule' like this? (Grice was the first person 
> to describe these rules for English, but he didnt impose them, they 
> seem to have just kind of happened.) It goes beyond the RDF or OWL 
> semantics, which don't say anything about web actions or agency. I 
> don't see the TAG group doing anything this formal-sounding in the 
> forseeable future, and I don't see that we have the authority to do 
> it. Maybe all we can do is to suggest that this might be a good way to 
> behave and hope that the world in general listens (?)

I think it should be sufficient to define the 'operational' 
specification
of how the bootstrapping intepretation is done, per the semantics of the
bootstrapping vocabulary within the context of a particular, named 
graph.

RDF/OWL applications that don't understand the special vocabulary will
not be impacted by statements using it, but those that do understand
the vocabulary will know how to perform the special bootstrapping
pre-interpretation of the graph to test assertion and authenticity
prior to any further RDF/OWL interpretation.

>
> Anyway, I'll send this off and see what happens :-)


Geee... what does this big red button do...?

;-)

Patrick


--

Patrick Stickler
Nokia, Finland
patrick.stickler@nokia.com

Received on Thursday, 11 March 2004 06:34:13 UTC