Title: RE: [xdi] Bill's suggestions
I've been doing some more thinking about the $data as datatype specifier concept, particularly in light of some comments by Dan Connolly and others with the gist that the RDF WG maybe should have used xsi:type instead of rdf:datatype (http://www.mnot.net/blog/2005/04/01/rdf_complexity).
It seems to me there are already two comprehensive methods for typing literal data, and the contents of <data> are essentially literals (Even XDI in there is still treated as an XML literal I think). Those two methods are xsi:type and mime type. It seems to me also that xsi:type and mime type are actually types of Strings themselves.
Based on that, I propose changing to the following:
+sometype+foo/$type.xsi/string
and @example/+sometype+foo//
Instead of
+sometype+foo/$is$a/$data+string
and @example/+sometype+foo//
Both state that the datatype of +sometype+foo is a string.
In addition, if I want to say that +sometype+foo is HTML we have a problem. We have limited ourselves to 3 segments, which I have no problem with, and an XREF has to have a root so we can't do (please correct me if I'm wrong on this):
+sometype+foo/$type.mime/(text/html)
If we use convention again and say that we are adopting the mime type identifiers, except that our mime type major/minor delimiter is . instead of / then we can write:
+sometype+foo/$type.mime/text.html
But what about the case where there are multiple alternate types? An example:
_:x rdf:type rdf:alt .
_:x _:1 "hello, world"^^xsd:string .
_:x _:2 "<p>hello, world</p>"^^rdf:XMLLiteral .
(above cribbed from Jimmy Cerra's comment at the page linked above, assume base of http://example.com)
This would be stated by the following XRIs ('data:' usage spur of the moment, and may need rethink):
@example*x/$type.mime/text.plain
@example*x/$type.mime/text.xml
@example*x/$type.mime/text.plain//data:text/plain,hello, world
@example*x/$type.mime/text.xml//data:text/xml,<p>hello, world</p>
Looking at this if we had any kind of inference mechanism we could streamline down to:
@example*x/$type.mime/text.plain//data:text/plain,hello, world
@example*x/$type.mime/text.xml//data:text/xml,<p>hello, world</p>
and have the valid existence of the other two XRIs inferred.
I don't like the combo of text.plain and text/plain in there, but not sure what to do about it right now.
Ok so we can state multiple data types, but can we retrieve them by type? Sure:
@example*x/($type.mime/text.plain)//
@example*x/($type.mime/text.xml)//
<uncertainty>
If we are still supporting both the s/p/o and the auth/type/inst (a/t/i) models, then we could even say that an XRI like
+sometype+foo/+name/+last
is by definition shorthand for
+sometype*foo/($type.xdi/+name)/+last
</uncertainty>
Which means that the XDI dictionary typing system possibly goes from the only way to do typing to just the recommended way to type non-literal XDI resources.
The above seems cleaner to me than the N3 RDF version, and way cleaner than the XML RDF version. Note that I have changed the meaning from the RDF version somewhat since it seems the multiple XRIs express an rdf:bag (agent may choose one or more of), rather than rdf:alt (agent may choose one of). Not sure how to resolve that yet.
Bill
-----Original Message-----
From: Drummond Reed [mailto:]
Sent: Thu 2/15/2007 2:01 AM
To:
Cc: Barnhill, William; ;
Subject: RE: [xdi] Bill's suggestions
Laurie, thanks for the reminder. To extract Bill's question, it was:
> But..is $data meant to represent actual data, or the datatype? Put
> another way, what is the relationship of
> @example+foo$data
> to
> @example+foo//
First I need to clarify that that $data is used to define datatypes as an
XDI RDF object XRI value, not as an XDI RDF subject, so I think the
appropriate question is, what is the relationship of:
+sometype+foo/$is$a/$data+string
to
@example/+sometype+foo//
What the first XDI RDF statement says is that the datatype of +sometype+foo
is a string. From that you know that any XDI RDF statement that uses
+sometype+foo as a predicate and has a literal as an object will have a
string as datatype of the literal.
More in the next version of the proposal coming shortly (either tonight or
tomorrow morning).
=Drummond
-----Original Message-----
From: [mailto:]
Sent: Tuesday, February 13, 2007 9:11 PM
To: Drummond Reed
Cc: 'Barnhill, William'; ;
Subject: Re: [xdi] Bill's suggestions
Drummond,
I apologize if you've already addressed this in the newest version of the
RDFX documentation, but I just wanted to follow up wrt Bill's question
about $data, given that I asked you a similar question last week. That is,
is $data meant to represent data or the data type?
And, if it is meant to represent data, how is the data type represented?
Cheers,
Laurie
> Bill,
>
> Thanks for the very helpful analysis of the RDF predicate mapping of the 5
> RDFX verbs. Paul Trevithick sent me a note with a similar analysis and I
> believe identical conclusions (we need time to study them closely).
>
> I also think that "as" is a brilliant suggestion as the English equivalent
> of the $data predicate. I kept wondering about that one and you nailed it
> on
> the head.
>
> See my next message about the recurring question of naming of the five
> predicates.
>
> =Drummond
>
> -----Original Message-----
> From: Barnhill, William [mailto:]
> Sent: Thursday, February 08, 2007 2:11 PM
> To: ;
> Subject: [xri] RE: [xdi] Re: [xri] Agenda: Joint XRI & XDI TC Telecon 4pm
> PT
> Thursday 2007-02-08
>
>
> I won't be able to attend the telecon, but wanted to post some thoughts
> on the RDFX doc:
>
> It would make seeing the RDF fidelity easier if the five root RDFX
> predicates table contains a column that maps to the equivalent RDF
> predicate, specifically:
>
> Predicate English Relationship RDF style Predicate
> $ref "is" equivalence
> owl:equivalentClass
> $ref$object "is a" inheritance rdf:type (if
> subj is an object, owl:class otherwise)
> $link "has" aggregation
> exns:hasXXX, where XXX is the property name specified within the link
> XRI
> $link$object "has a" composition exns:xxx, where xxx is
> the property type specified within the link XRI
> $data "" datatype
> rdf:parseType
>
> I'd also suggest an English phrase for data: "as", ex: "as String"
> But..is $data meant to represent actual data, or the datatype? Put
> another way, what is the relationship of
> @example+foo$data
> to
> @example+foo//
>
>
> Exns is the prefix for a domain-specific namespace.
>
> On the 3 col graph, I like it, though I'd like to see it bigger to
> labelling is clearer.
>
> On tightening the XRI syntax within the schema there's a fairly easy way
> that makes it clear, and doesn't impose a further burden on
> implementers, but does allow them to do automated checking if they want:
> use schematron extensions within the schema.
>
> Bill
>
>
