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Subject: Re: [xdi] Re: XDI subjects (was Groups - XDI RDF v8 Comments-Barnhill)
There are at least three reasons, in my opinion, why XDI/RDF subjects
can't be literals:
1) RDF itself doesn't allow literals as subjects:
http://www.w3.org/TR/rdf-concepts/#dfn-subject
2) The proper XDI mapping of:
Blah blah <a href="http://example.com/some/target";>some literal text
here</a> blah blah
would be:
XDI subject = "http://example.com/some/target";
XDI predicate = $html$a
XDI object = "some literal text here"
and the corresponding inline X3, with the additional predicates in
Drummond's example, would be something like:
Blah blah [http://example.com/some/target[$html$a["some literal text
here"]] [$uri$https[https://example.com/resolvable/uri]][$is[@!F83.62B1.44F.2813!1234]]
blah blah
3) Allowing literals as subjects doesn't make logical sense. Consider
the following:
<"http://example.com/number/of/hours/in/a/day";>
<http://english.com/is";> <"24">.
<"http://example.com/number/of/beers/in/a/case";>
<http://english.com/is";> <"24">.
So far, so good. But to assert the following:
<"24"> <"http://english.com/is";>
<"http://example.com/number/of/hours/in/a/day";>.
<"24"> <"http://english.com/is";>
<"http://example.com/number/of/beers/in/a/case";>.
is to assert some substantial connection between the number of hours
in a day and the number of beers in a case, which is fallacious.
=Kermit
On 3/18/08, Drummond Reed <drummond.reed@cordance.net> wrote:
>
>
>
>
> First, let me be clear: I'm not a big fan of using literals as subjects, and
> I don't have any compelling use cases for it (see below for the only one
> I've been thinking about). It was Giovanni who seemed to have a reason for
> using literals as subjects.
>
>
>
> Second, I agree, a literal as a subject can't be changed or it becomes a new
> subject from an XDI standpoint.
>
>
>
> Now, here's the one thing that's had me thinking about literals-as-subjects
> for a long time – take a standard HTML link tag:
>
>
>
> Blah blah <a
> href="http://example.com/some/target";>some literal text
> here</a> blah blah
>
>
>
> If you wanted to turn this into an XDI statement, the only logical mapping
> that seems to make sense is:
>
>
>
> XDI subject = "some literal text here"
>
> XDI predicate = $uri
>
> XDI object = "http://example.com/some/target";
>
>
>
> In other words, were you to replace HTML <a> tags with X3 within an HTML
> document, the above link would look like:
>
>
>
> Blah blah ["some literal text
> here"[$uri["http://example.com/some/target";]]] blah blah
>
>
>
> That's pretty cool, because now you have a way of embedding really rich
> semantics into ordinary web pages and web links. As a simple example, image
> being able to make the above simple link into a compound statement, which
> includes: a) an alternate HTTPS URL for the target resource, and b) a
> persistent XRI synonym for the resource:
>
>
>
> Blah blah ["some literal text
> here"[$uri["http://example.com/some/target";]]
> [$uri$https["https://example.com/some/target"]][$is[@!F83.62B1.44F.2813!1234]]
> blah blah
>
>
>
> Net net: it's the ability to put XDI statements inline in ordinary HTML and
> other markup formats that's the strongest use case I've seen so far for
> being able to treat literals as XDI subjects.
>
>
>
> =Drummond
>
>
>
>
>
>
> ________________________________
>
>
> From: markus.sabadello@gmail.com [mailto:markus.sabadello@gmail.com] On
> Behalf Of Markus Sabadello
> Sent: Tuesday, March 18, 2008 9:30 AM
> To: Drummond Reed
> Cc: Giovanni Bartolomeo; barnhill_william@bah.com; xdi@lists.oasis-open.org
> Subject: [xdi] Re: XDI subjects (was Groups - XDI RDF v8 Comments-Barnhill)
>
>
>
>
>
> One aspect that seems strange with using literals as subjects is that you
> can't modify them with XDI messages (I think).
>
> If you have
>
> =drummond
> +name
> "Drummond"
>
> You can modify the literal like this:
>
> =drummond
> $mod
> /
> =drummond
> +name
> "D.Reed"
>
> But you can't modify a subject.
>
> What again was a use case for literals in subjects? (I'm not against it,
> just asking)
>
> Markus
>
>
> On Mon, Mar 17, 2008 at 7:34 PM, Drummond Reed <drummond.reed@cordance.net>
> wrote:
>
>
>
> [renaming this thread to something more relevant]
>
>
>
> Giovanni,
>
>
>
> I agree with Markus – I can't make sense of having an XDI document as an XDI
> subject. I'm not sure my point from my earlier message came across, but I
> was saying that when you use XDI context syntax – the // syntax – it does
> _not_ assert that the previous XDI document is the subject of an XDI
> statement. It says that the previous XDI statement _contains_ another XDI
> statement. For example, in the following X3 Simple graph…
>
>
>
> =drummond
>
> +email
>
> /
>
> =drummond
>
> +email+home
>
>
> "dsr.example@gmail.com"
>
> +email+work
>
>
> "drummond.example@cordance.net"
>
>
>
> …you can make the following "compound XDI statement":
>
>
>
> =drummond/+email//=drummond/+email+home
>
>
>
> This compound statement does not assert an XDI document as a subject. It
> asserts the following:
>
>
>
> 1) =drummond is an XDI subject
>
> 2) +email is an XDI predicate of this subject
>
> 3) The object is another XDI document
>
> 4) =drummond is an XDI subject in this contained XDI document
>
> 5) +email+home is an XDI predicate of that XDI subject
>
> 6) "dsr.example@gmail.com" is the literal value of that XDI object
>
>
>
> If you wanted to have an entire XDI document as the subject of an XDI
> statement, I think the syntax you are looking for is:
>
>
>
>
> (xdi-subject/$context$xdi)/xdi-predicate/xdi-object
>
>
>
> In this XDI statement:
>
>
>
> 1) (xdi-subject/$context$xdi) is a cross reference that uniquely identifies
> an XDI document:
>
> a) xdi-subject is the XDI subject authoritative for a reference
> to the XDI document
>
> b) $context$xdi is the context type
>
> 2) xdi-predicate is the XDI predicate whose subject is the entire previous
> cross-reference
>
> 3) xdi-object is whatever the XDI object is (literal, another XDI subject,
> or another XDI document)
>
>
>
> ****************
>
>
>
> As for the issue of whether a literal can be an XDI subject, my primary
> concern about that is how to treat it under XDI addressing rules. In every
> XDI context, the XRIs must be unique. So there are two directions we could
> take:
>
>
>
> 1) Allow literals to be XDI subjects, but ignore them from an XDI addressing
> perspective (i.e., they would be "invisible" from an addressing standpoint.)
>
>
>
> 2) Allow literals as XDI subjects in syntax, but for addressing purposes,
> have a specified transformation into relative XRI. For example:
>
>
>
> ["Drummond Reed"[+email[""dsr.example@gmail.com"]]] <==X3 with literal as
> non-addressable subject
>
> [%44rummond%20%52eed[+email[""dsr.example@gmail.com"]]] <==X3 with literal
> as addressable XRI subject
>
>
>
> Thoughts?
>
>
>
> =Drummond
>
>
>
>
>
>
> ________________________________
>
>
> From: markus.sabadello@gmail.com [mailto:markus.sabadello@gmail.com] On
> Behalf Of Markus Sabadello
> Sent: Monday, March 17, 2008 9:10 AM
> To: Giovanni Bartolomeo
> Cc: Drummond Reed; barnhill_william@bah.com; xdi@lists.oasis-open.org
> Subject: Re: [xdi] Groups - XDI RDF v8 Comments-Barnhill (pdf) (XDI RDF v8
> Comments-Barnhill.pdf) uploaded
>
>
>
>
> From the standpoint of having already implemented this, the proposal of
> allowing a subject to be an XDI document (aka subcontext aka inner graph) is
> a nightmare..
>
> I can think of at least the following immediate problems:
> - Some of the serialization formats may not be able to express this.
> - We always said that subjects in a graph must be unique. Can this still be
> enforced with inner graphs as subjects?
> - What will XDI messages look like that make changes to these subjects?
>
> I don't feel too secure about allowing literals as subjects either, but I
> can't really argue why at this point..
>
> But I'm just thinking loud.. Of course all this is not necessarily a reason
> not to do it :)
>
> Markus
>
>
> On Sat, Mar 15, 2008 at 1:39 PM, Giovanni Bartolomeo
> <giovanni.bartolomeo@uniroma2.it> wrote:
>
>
>
> At 20.52 13/03/2008, Drummond Reed wrote:
>
> Giovanni,
>
> It's a subtle point, but when you use subcontext syntax (//), the parent
> XDI document is not the subject of the child XDI document. It is the
> container ("context") for the child. Thus I don't think the ABNF should
> change.
>
>
>
>
> Ok, I see; so if my understanding is correct, we have both the possibility
> to have a whole XDI document as an RDF object as well as a "contained"
> object ("subcontext"). Thus, the original question: in these ABNF excerpts,
> how could we specify that a subject can be an XDI document? E.g.
>
>
>
> X3 = *( "[" sub *( "[" pred *( "[" obj "]" ) "]" ) "]" )
> sub = [ comment ] xri-reference [ comment ]
> sub = [ comment ] (xri-reference / X3) [ comment ]
> pred = [ comment ] xri [ comment ]
> obj = [ comment ] ( xri-reference / literal / X3 ) [ comment ]
> literal = """ *char """
> comment = "<--" *c-char "-->"
>
>
>
> RE the question of whether to allow a literal as an XDI subject, yes, I have
> thought about, for reasons which I'll explain on today's call (if we have
> time).
>
>
>
> I would allow this; especially if we'll standardize inverse predicates, we
> should allow a subject to be a literal, as well as a XDI document or a
> xri-reference.
>
>
>
>
>
>
>
> RE whether a predicate should be able to be an XDI document, my immediate
> answer is no – RDF predicates are strictly URIs; XDI predicates should be
> strictly XRIs.
>
>
>
> Yes, I agree with this. To summarize, I would be in favour of having the
> same definition for subjects and objects:
>
> sub = [ comment ] (xri-reference / literal / X3) [ comment ]
>
>
> pred = [ comment ] xri [ comment ]
> obj = [ comment ] ( xri-reference / literal / X3 ) [ comment ]
>
> what do you think?
>
> Thanks,
> Giovanni
>
>
>
>
>
>
>
>
> Talk to you shortly,
>
> =Drummond
>
> ________________________________
>
>
> From: Giovanni Bartolomeo [
> mailto:giovanni.bartolomeo@uniroma2.it]
> Sent: Thursday, March 13, 2008 3:11 AM
> To: Drummond Reed; 'Markus Sabadello'
> Cc: barnhill_william@bah.com; xdi@lists.oasis-open.org
> Subject: RE: [xdi] Groups - XDI RDF v8 Comments-Barnhill (pdf) (XDI RDF v8
> Comments-Barnhill.pdf) uploaded
>
> Hello Drummond,
>
> Thanks for this clarification; however, if my understanding is correct,
> this means that an XDI document can also be subject of another XDI document,
> other than object.
> Doesn't this implies that we should update ABNF syntax making the
> definition of subject somehow similar to the one for object?
>
> X3 = *( "[" sub *( "[" pred *( "[" obj "]" ) "]" ) "]" )
> sub = [ comment ] xri-reference [ comment ]
> sub = [ comment ] (xri-reference / X3) [ comment ]
> pred = [ comment ] xri [ comment ]
> obj = [ comment ] ( xri-reference / literal / X3 ) [ comment ]
> literal = """ *char """
> comment = "<--" *c-char "-->"
>
> Further questions are:
>
> should allow literals as a subject?
> should be predicate definition similar to subject and object one
> update, e.g. may a predicate contain an XDI document?
>
> however I'm not quite convinced with these last two ideas... comments
> welcome!
>
> Giovanni
>
>
> At 22.38 12/03/2008, Drummond Reed wrote:
>
> Just to be clear, the "n-segment" syntax was deprecated in the V9 XDI RDF
> Model document (
> http://wiki.oasis-open.org/xdi/XdiRdfModel) due to the
> problems identified in this thread. To be precise, it was unclear whether
>
> s1
> p1
> o1
> p2
> o2
>
> meant that s1/p1/o1 was the subject of p2/o2 or not. It was also unclear
> how cross-reference syntax would be applied.
>
> We solved both problems by eliminating "n-segment" syntax in the V9
> document. Now it should be unambiguous that if you want to express that
> s1/p1/o1 is the subject of p2/o2, you say:
>
> (s1/p1/o1)/p2/o2
>
> What did remain is the // syntax for subcontexts, which allows you to solve
> the RDF "blank node problem" by providing an address for a blank node. That
> address is simply // (which fits very nicely from a conceptual standpoint
> since the identifier for that segment is "blank").
>
> So if I want to say that the object of s1/p1 is a blank node, I can write
> it as s1/p1// . This creates a new XDI context in which I can express
> another set of XDI statements whose XRIs are unique in this context.
>
> We'll go over the practical uses for this on the call tomorrow – agenda
> coming out shortly.
>
> =Drummond
>
> ________________________________
>
>
> From: markus.sabadello@gmail.com [
> mailto:markus.sabadello@gmail.com] On Behalf Of Markus
> Sabadello
> Sent: Wednesday, March 12, 2008 10:44 AM
> To: Giovanni Bartolomeo
> Cc: barnhill_william@bah.com; xdi@lists.oasis-open.org
> Subject: Re: [xdi] Groups - XDI RDF v8 Comments-Barnhill (pdf) (XDI RDF v8
> Comments-Barnhill.pdf) uploaded
>
>
> To be honest, I don't really understand the N-Segment syntax anyway.
>
> Why is
>
> s1
> p1
> o1
> p2
> o2
>
> better than
>
> s1
> p1
> o1
> o1
> p2
> o2
>
> ?
>
> Markus
> On Tue, Mar 11, 2008 at 4:29 PM, Giovanni Bartolomeo <
> giovanni.bartolomeo@uniroma2.it> wrote:
> Dear Bill, All,
>
> reading your comments about XDI RDF v8 (
> http://www.oasis-open.org/committees/download.php/27112/XDI%20RDF%20v8%20Comments-Barnhill.pdf
> ) I've found this sentence:
>
> One problem with the 3-Segment syntax is that the N-Segment syntax uses
> cross-references for
> reification. This means 3-Segment syntax has to have a different notation
> for a subject which is the
> statement itself rather than the object of the statement. The 3-Segment
> notation for this is a crossreference
> within a cross-reference: (()). So a subject of (s/p/o) asserts s/p/o and
> starts a new statement
> whose subject is o, while a subject of ((s/p/o)) asserts s/p/o and starts a
> new statement whose subject is
> the statement s/p/o. For example to say that =Drummond is author of the
> statement =Bill.Barnhill is a
> contributor to the resource represented by @example we would use the XRI:
> ((@example/+dc+contributor/=Bill.Barnhill))/+dc+author/=Drummond.
>
> Well, I'm wondering how N3 syntax (and consequently X3 simple) addresses
> this problem:
>
> If my understanding is correct, the N3 syntaxt
> <s1> <p1> <o1>
> <o1> <p2> <o2>
> is equivalent to X3 simple
> s1
> p1
> o1
> p2
> o2
> what if I want to express that the whole statement <s1> <p1> <o1> is the
> subject of <p2> <o2>? How this can be represented with X3 Simple?
> Breaking into a new subcontext doesn't seem to help, as this explicitly
> introduce a new subject!
> s1
> p1
> /
> s2
> p2
> o2
>
> Whereas I just want that the whole statement (s1/p1/o1) is the subject of
> p2!
>
> What do you think? Am I missing something?
>
> Thanks,
> Giovanni
>
>
> At 11.06 07/02/2008, barnhill_william@bah.com wrote:
>
> The document named XDI RDF v8 Comments-Barnhill (pdf) (XDI RDF v8
> Comments-Barnhill.pdf) has been submitted by Mr. William Barnhill to the
> OASIS XRI Data Interchange (XDI) TC document repository. Document
> Description: View Document Details:
> http://www.oasis-open.org/apps/org/workgroup/xdi/document.php?document_id=27112
> Download Document:
> http://www.oasis-open.org/apps/org/workgroup/xdi/download.php/27112/XDI%20RDF%20v8%20Comments-Barnhill.pdf
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