Re: RDF* semantics

Marco, Thomas,

> But you have heard of "social meaning", right?

I have, and I agree with you that formal semantics can not (and is not
meant to) capture the whole depth and subtlety of human/social meaning. I
maintain my argument, though, that *what falls in the scope of formal
semantics* is less ambiguous in such languages than in natural languages.

Now, my understanding of this thread was that it was about the formal
semantics of RDF*, not any social meaning that *could* be built on top of
it. And I still do not think that the distinction between a Person and a
Statement about that person is out of scope for the formal semantics...

On Mon, 2 Sep 2019 at 13:13, Marco Neumann <marco.neumann@gmail.com> wrote:

>
> 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
>
>