Re: RDF* semantics

On Mon, Sep 2, 2019 at 12:02 PM thomas lörtsch <tl@rat.io> wrote:

> > On 2. Sep 2019, at 11:15, Pierre-Antoine Champin <
> pierre-antoine.champin@univ-lyon1.fr> wrote:
> >
> > Dear Thomas,
> >
> > I have to strongly disagree with you.
> >
> > On Fri, 30 Aug 2019 at 18:16, thomas lörtsch <tl@rat.io> wrote:
> >> We are on the Semantic Web here which in general is not aiming at such
> subtleties. The semantics of identification in RDF are vague at best. Does
> https://paris.com refer to the website or the city?
> >
> > The semantics of identification is *not* vague. It is precisely defined
> in the RDF Semantics [1] specification. You can also refer to the RDF
> Concepts [2] spec, section 1.3. It clearly talks about "the resource
> denoted by an IRI" (note the *singular* use of "resource").
>
> But you have heard of "social meaning", right?
>

just a random observation I had a similar conversations since 2001 and
ongoing. It's why the name Semantic Web is somewhat unfortunate. If
anything it's The Formal Semantic Web and it would have been a better
choice as a name. I now prefer to think of it as Linked Data plus logic.
It's certainly it's not the Social Semantic(s) Web.

RDF* semantics seems to fall into the same trap here. So I better think of
this as the RDF* formal semantics thread.



>
> > I'm not saying that it is always easy to decide what exactly an IRI
> identifies. Especially with HTTP IRIs, which intuitively identify web
> resources (i.e. digital objects) rather than persons or city. There has
> been a long controversy [3] in the community about that, but it has been
> settled. For example, http://dbpedia.org/resource/Lyon identifies a city,
> while http://dbpedia.org/page/Lyon identifies the HTML document
> describing that city.
>
> I wasn’t aware of that settlement. I don’t think it ends the debate about
> how to disambiguate denotation from indication on the semantic web in
> general. Note also that further scrutiny (or zealotry?) could demand to
> disambiguate the web page from the web site, the historic city center from
> some modern times administrative area etc etc. Note also that the other
> examples I gave are still unresolved. So, the semantics of RDF are vague in
> contrast to the subtle differentiations that natural language can express
> and they’ll always be. It’s a formalism - that brings abstractions with it,
> and abstractions cut off detail and sublime differentiations. That’s the
> whole point of it. Re-introducing those subtleties has a high risk of being
> arbitrary and rather limit exchange of information than facilitate it.
> Introducing limits may of course be useful but in the case of blank nodes I
> don’t think it is. IMO they should be handled as liberal as possible (of
> course some *added* on-demand disambiguation notwithstanding which is what
> I’m working on).
>
> > However, in the example at hand, there is no ambiguity:
> >
> > _:b1 rdf:type :Person.
> > _:b1 :name "Alice".
> > _:b1 :asserts _:b2.
> > _:b2 rdf:type :Person.
> > _:b2 :name "Bob".
> >
> > the 4th triples says it clearly: _:b2 identifies something of type
> Person. If we agree that Persons and Statements are different kinds of
> animals, then we can not possibly interpret this graph as "Alice assertin
> some statement about…".
>
> Well, I think we could interpret the identification semantics of_:b2 as
> either denoting some statements or as indicating what those statements
> describe (or of course its own shere existance but let’s try to not get
> into any more ratholes). Like any other URI that has not been disambiguated
> through the dbpedia settlement mechanism that you refer to above this one
> relies on "social meaning" and out of band agreement, maybe through
> convention or intuition about "naturalness" or specified by the range of
> the property used.
>
> In the example at hand I read:
> "Alice asserts that a person named Bob exists"
> or, to avoid the discussion about ’that’ that I had with Olaf:
> "Alice asserts: a person named Bob exists"
> or, to avoid the connotation of serious logic:
> "Alice asserts a person Bob".
> That third example however doesn’t sound right in english. There is a
> msimatch between english and RDF - which is rather unsurprising as
> formalisms are languages of their own and tend to have their own subtle
> ways.
> Now, what do *you* want to speak about - the person Bob or Alices
> statement? Both is possible.
>
> > Later you wrote:
> >> This needs disambiguation even in plain english not to speak of RDF.
> RDF is not meant and can’t reasonably be expected to express such
> subtleties.
> >
> > The primary goal of *formal* languages is precisely to be less ambiguous
> than natural languages. So yes, RDF should be expected to carry less
> ambiguity than english prose.
>
> Isn’t this a rather naive take on the nature of formalisms? I guess we are
> all aware of the high hopes in logic - Leibnitz' "Calculemus!" - and the
> modest results so far. So what should or might be expected is not always
> what we get. RDF however is not even aiming to be AI, it is a toolset that
> e.g. relies on shared understanding about the meaning of the vocabulary
> used. It’s a pity that one of its basic constructs, the blank node, has led
> to so much confusion and discontent however it is also not really
> surprising. RDF tries to simplify things to make them amenable to
> ubiquituous use at unprecedented scale. With such a design goal some
> details get inevitably lost in translation.
> We could (try to) enforce the very strict semantics that you and Olaf
> demand but I don’t think that’s a good idea. This is a Hydra that grows 2
> new heads for every one you cut off. If the issue is not pressing better
> leave it alone.  I rather advocate an approach that allows to express such
> specifics on demand, like: if I need to make sure that some blank node is
> understood in a certain way I’d like to have some syntactic sugar and
> vocabulary at my disposable to do so.
>
> >> If I wasn’t too lazy I would now check the RDF specifications as I’m
> sure there’s citable proof that blank nodes in RDF are not a means to speak
> about the shere existance of certain things
> >>
> > RDF Semantics [1],  section 5.1, first sentence:  "Blank nodes are
> treated as simply indicating the existence of a thing".
> > You couldn't have chose better words -- except for "not", obviously ;-)
>
> No, because you are missing the most important word in that sentence:
> "simply" :-) This precisely tries to convey the intuition that one
> shouldn’t interpret too much into blank nodes. RDF is much to simple,
> simplistic even, to carry the meatphysical load that you and Olaf want it
> to carry. Blank nodes are used as existential quantifiers with all the
> logical consequences that come with it but they are also used as mere
> anchor points to collect a few properties of something that is not meant to
> get its own URI. A good example is
>         :Bob :hasAdress [ :street "abc-street 1"; :city "Hometown"; :zip
> 12345 .]
> Usually nobody would want to get philosophical about that blank node and
> the sort of existential questions that can arise from it. In other
> situations they are used exactly for the purpose of discussing existential
> questions of existance. It depends. I’d say Postels law - "Be liberal in
> what you accept…" - applies here in slightly modified form: "Be liberal in
> what you expect a blank node to express". Or, in other words: curb your
> enthusiasm ;-)
>
> Olaf’s initial critique of Kingsley’s proposal already showed the
> difficulties that arise when we interpret too much in RDF structures: he
> interpreted the blank node in the object position different from the blank
> node in the subject position of Kinglsey’s example. It only got worse from
> there when he drew a conclusion about the range of :claims - the slightly
> bizarre ownership interpretation - from the syntactic structure of the
> object alone. This is precisely what I critcize: RDF doesn’t support such
> subtleties. It has blank nodes, reification of statement types (but not
> tokens) and in a hackish way also graphs. How much expressivity can you
> expect from that on its own? Of course you can model everything with the
> help of suitable classes and properties but in and on itself RDF is very
> limited and barely express some structure in the sea of triples. Relying on
> that structure to transport a lot of meaning leads into dangerous
> territories of - and that is an empirical fact that you can gather from
> countless threads like this one on semantic web related mailing lists -
> undissolvable disputations about the semantics of this, that and "but no I
> meant *that*". That's the exact opposite of easy interoperability that the
> Semantic Web is meant to enable.
>
> Thomas
>
> >   pa
> >
> > [1] https://www.w3.org/TR/rdf11-mt/
> > [2] https://www.w3.org/TR/rdf11-concepts/
> > [3] https://en.wikipedia.org/wiki/HTTPRange-14
> >
> > Does a graph name name or label the graph? Is a statement reification
> referring to a type of statement or a statement token of that type? Cowpath
> defaults and "social meaning" rule at every level of identification in RDF
> and in general I think that in its alternativelessness this is a big
> problem and needs to be solved. However I think it needs to be solved
> through defaults and on demand disambiguation - late binding if you will -
> , not through arbitrary descents into semantic rat holes and tedious
> disambiguation when it isn't needed.
> > The default mode of the Semantic Web is straightforward exchange of
> facts like "there's a person named Bob of age 23 and alice, also a person,
> claims something about him". A blank node is nothing more than a structural
> helper, the semantic equivalent of a throw away plastic bag (I know we
> don't do that anymore although we have conferences at the end of the world,
> 11800 kg of CO2 from northern germany by plane). "There exists..."
> yadayada. The most intelligent thing you can teach your dumb machine to do
> is treat these facts at face value. Further subtleties may be encoded in
> the vocabulary: some specific Alice vocabulary may define alice:claims to
> have domain slaveholder and range slave as Olaf suggested.
> > If you want to speak about the fact as it has been stated (provenance
> etc) you need to reify it. Concise syntax and appropriate semantics would
> help as I like to keep repeating. To RDF the person and the fact are both
> just subjects of discourse, resources referenced by URIs. To RDF there is
> no difference here. Which has the fine property of making endlessly nested
> meta-meta-meta-... constructs possible - which is probably the least we
> would need to model this conversation in RDF.
> > But maybe you are not even suggesting to distinguish indication and
> denotation but want to speak about something like the factuality of that
> fact, no matter if or by whom it was stated? I wouldn't be able to follow
> you there - to dangerous... ;-)
> >
> > >Second, RDF semantics is defined under the Open World Assumption:
> > >whatever
> > >you know about a given node, you have to assume that there *may* be
> > >other
> > >triples about that node that you are not aware of. So by the "sum of
> > >its
> > >attributes", do you mean "everything that is true about the node,
> > >whether
> > >you know it or not" (which would be consistent with the OWA), or
> > >"everything that is stated in a given graph" (which would seem more
> > >appropriate for representing a give claim by Alice)?
> >
> >
> > That's an orthogonal question. Named Graphs could help if their
> semantics are properly specified (easy, just define an appropriate
> vocabulary, and use the RDF extension mechanism to define a suitable
> semantics).
> >
> >
> > Thomas
> >
> >
> > >  pa
> > >
> > >On Fri, 30 Aug 2019 at 11:46, thomas lörtsch <tl@rat.io> wrote:
> > >
> > >>
> > >>
> > >> > On 30. Aug 2019, at 10:29, Olaf Hartig <olaf.hartig@liu.se> wrote:
> > >> >
> > >> > Hi Thomas,
> > >> >
> > >> > On torsdag 29 augusti 2019 kl. 10:18:48 CEST thomas lörtsch wrote:
> > >> >> [...]
> > >> >> Ah, you are really taking all those little ’that’ words very
> > >serious ;-)
> > >> >
> > >> > I better do; we are talking about semantics here ;-)
> > >> >
> > >> >> [...] your translation, "a person Bob who is of age 23", captures
> > >the
> > >> sense
> > >> >> of factualness even better.
> > >> >
> > >> > Good.
> > >> >
> > >> >>> Therefore, all the triples together seem to say that a person
> > >named
> > >> >>> Alice claims a person named Bob who is of age 23. My initial
> > >example
> > >> >>> said something else, namely: person Alice claims *that* person
> > >Bob is
> > >> of
> > >> >>> age 23.
> > >> >>
> > >> >> Hmm, that *that* again ;-) So you mean the difference between
> > >Alice
> > >> claiming
> > >> >> that there exists a "Bob, person, aged 23" and Alice claiming that
> > >some
> > >> >> already introduced and agreed upon person Bob is "aged 23"?
> > >> >
> > >> > While the fact that the person Bob has already been introduced and
> > >> agreed upon
> > >> > is necessary to make single-statement claims about this person,
> > >this is
> > >> > secondary to the main point I keep on trying to make. Again, in my
> > >> opinion,
> > >> > Kingsley's data cannot be interpreted as you do in your sentence
> > >above
> > >> (person
> > >> > Alice claims "that there exists" a person Bob of age 23). In
> > >contrast,
> > >> since
> > >> > bnode _:b2 represents 'a person Bob of age 23', the :claims triple
> > >with
> > >> _:b2
> > >> > in the object position is to be interpreted as: person Alice claims
> > >the
> > >> person
> > >> > Bob (rather than claiming the existence of such a person). Hence,
> > >the
> > >> verb
> > >> > "claim" here is used with its meaning of demanding ownership
> > >instead of
> > >> its
> > >> > meaning of stating (potentially false) facts. See:
> > >> >
> > >> > https://en.wiktionary.org/wiki/claim#Verb
> > >>
> > >> Well, so "claims" has more meanings then that usually assumed in the
> > >> context of semantic web discussions about reification, provenance
> > >etc.
> > >> However: either Alice claims the existence or ownership of "a person
> > >Bob
> > >> who is of age 23". I don’t see what difference this makes with
> > >respect to
> > >> our discussion about RDF* etc. Anyway I wouldn't want the semantics
> > >of some
> > >> property to have such wide ranging consequences on the meaning of
> > >basic
> > >> structural constructs like a blank node (… amybe a bit too bold a
> > >statement
> > >> - I hope there aren’t any non-marginal counter examples proofing me
> > >wrong).
> > >>
> > >> > If you would only want to capture that person Alice claims "that
> > >there
> > >> exists"
> > >> > a person Bob of age 23, then the object of the :claims triple
> > >cannot be
> > >> the
> > >> > bnode _:b2, but instead the object needs to be a graph that
> > >contains the
> > >> three
> > >> > triples that have bnode _:b2 in their subject position.
> > >>
> > >> That’s quite strong as a requirement. As I said before: what else
> > >could a
> > >> blank node possibly mean then the sum of its attributes? Can you give
> > >a
> > >> convincing answer to that question? And with convincing I mean
> > >"obvious",
> > >> "intuitive", "in wide use". One might want to talk about the blank
> > >node
> > >> *itself* but that is really a corner case and there are much wider
> > >gaps in
> > >> the identification semantics of the Semantic Web that would need a
> > >fix
> > >> first.
> > >> I think the other way round - you have to be specific if you want to
> > >> address the triple, otherwise you address all that’s said about the
> > >blank
> > >> node - is practicable and unsurprising. We have to find idioms that
> > >are
> > >> easy to use and have intuitive defaults. There is never an end to
> > >even more
> > >> precision but that doesn’t scale.
> > >> What I would endorse however is rather an 80/20 style approach like a
> > >> specific property to talk about the blank node itself - sensible
> > >defaults,
> > >> specific instruments where required. Disambiguating identification is
> > >also
> > >> a case by case problem: identifiers play different roles in different
> > >> situations. Concise statement attribution could make it feasible to
> > >> disambiguate those roles when necessary. That would be great.
> > >>
> > >>
> > >> Thomas
> > >>
> > >>
> > >>
> > >> >> Technically that is the difference between talking about a set
> > >> >> of triples with the same subject (lines 4-6 in the above example)
> > >and a
> > >> >> single triple (line 6), right?
> > >> >
> > >> > Almost. See above.
> > >> >
> > >> > Best,
> > >> > Olaf
> > >> >
> > >> >
> > >> >>>> [...]
> > >> >>>> However I would also like to stress that such modelling is not
> > >> >>>> meta-modelling and it is not equivalent to a layer of
> > >abstraction
> > >> >>>> (vulgo taking one step back) like reification or named graphs.
> > >> >>>
> > >> >>> Exactly! That's the point I am trying to make with this example.
> > >To
> > >> >>> capture the statement that "Alice claims *that* Bob is of age
> > >23," we
> > >> >>> need a form of meta-modeling.
> > >> >>
> > >> >> And I just wanted to express my endorsement of your position in
> > >that
> > >> >> respect.
> > >> >>>> [...]
> > >> >>>> Well, as I’m on it, a shameless plug: I recently posted an
> > >unhaelthily
> > >> >>>> long mail to this list . That mail started with [...] I wonder
> > >if
> > >> anybody
> > >> >>>> bothered to read that sermon.
> > >> >>>
> > >> >>> I did ;-)
> > >> >>
> > >> >> Great! :-)
> > >> >>
> > >> >>> ...and I was planning to respond to it. However, since I am on
> > >this
> > >> list
> > >> >>> here in my spare time, I couldn't get to it right away.
> > >> >>
> > >> >> No pressure! ;-)
> > >> >>
> > >> >> Thomas
> > >> >>
> > >> >>> Olaf
> > >> >
> > >> >
> > >>
> > >>
> > >>
>
>
>

-- 


---
Marco Neumann
KONA