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Subject: RE: [xri] POWDER on track to become proposed recommendation
Bill, POWDER has been on the XRI TC’s
radar since the start of the XRD work. It is one of the two example discovery
formats mentioned in Eran’s HTTP-Based Resource Descriptor Discovery spec
[1]. It is a more general descriptor format than XRD designed to make it easier
to supply RDF descriptions of sites. Thus it should be complementary to both
XRD and XDI. =Drummond [1] http://www.ietf.org/internet-drafts/draft-hammer-discovery-01.txt From: Barnhill,
William [USA] [mailto:barnhill_william@bah.com] What are the group's thoughts on
relevance of POWDER (http://www.w3.org/2007/powder/)
to XRI and XDI work? The POWDER group started as far as I can tell a little
over a year ago, but they say they are currently in process of transitioning to
a proposed recommendation. If this becomes a PR it might have an impact
on XRI/XDI adoption/voting, which is why I wanted to hear what your thoughts
are. An example of a POWDER document is: <powder xmlns="http://www.w3.org/2007/05/powder#" xmlns:ex="http://example.org/vocab#">
<attribution> <issuedby src=""http://authority.example.org/company.rdf#me"" /> <issued>2007-12-14T00:00:00</issued> <abouthosts>example.com</abouthosts> </attribution>
<ol>
<dr> <iriset> <includehosts>example.com</includehosts> <includepathstartswith>/foo</includepathstartswith> </iriset> <descriptorset> <ex:color>blue</ex:color> </descriptorset> </dr>
<dr> <iriset> <includehosts>example.com</includehosts> </iriset> <descriptorset> <ex:color>red</ex:color> </descriptorset> </dr>
</ol>
</powder> Regards, =Bill.Barnhill From: Barnhill,
William [USA] This is just initial thoughts as I'll look at the updated
diagrams/pages this weekend. For XDI graph with no metagraph statements and metagraph, why don't be
just paraphrase RDF? XDI Graph - An XDI graph is the union of a possibly empty A-Graph
containing XRIs that make statements about a set of individuals and/or
concepts, with a possibly empty T-Graph containing XRIs that make
statements about the statements contained within the A-Graph or statements
about the graph. ********** You said that +x/$has/+y does in fact
translate into two base graph statements: +x/+y/+x+y and +x+y But what do you mean by translate? Do you
mean (a) that the presence of thefirst in the graph implies the other two; (b)
that the presence of the other two in the graph implies the first, or (c) both? I agree with (c) for the +x+y part, but am
having trouble with the other. If you say (c) for both then +x/+y/+x+y
<=> +x+y. So the subject +ball, predicate +color has the object
+ball+color as well as +red? That would mean that a query of +ball/+color
would return two answers: +ball+color and +color*red? If +ball+color
and +color*red are synonyms then a query can have something similar to a
DISTINCT clause that eliminates synonymous XRIs. By synonyms I mean the
symmetric difference of the set of XDI nodes addressed by +x+y and the set of
XDI nodes addressed by +color*red. That would present the
following problems I think: .. There may be other things that are
colored red (e.g. +z/+y/+red) .. If the predicate +y does not have
a maxCardinality of 1 then there may be other colors for +x (e.g. +x/+y/+green) But for the above reasons I'm a lot more
comfortable with the RDF/OWL syntax I gave in the previous email as the
RDF analog to +x+y, which interprets +x/$has/+y as a property restriction on
the class of things +x. If you kind of combined what I'm understanding your
approach to be with my take one possibility might be: +ball+color <=> [+ball/+color/$$A ^
$$A/$a/+ball+color ^ +ball+color/$a/+color] This incorporates +x/$has/+y infers the statement +x+y/$is$a/+y as well as your other statements but
separates things from all being about individuals to some of the implied
statements being about class membership. What do you think? ***** One thing that's missing from the above
merged proposal is the $is. I don't have any reason other than that for me
it violates the principle of least surprise, but I really do not like $is as
the inverse operator, even less so than I liked $a. To me a different
set of metagraph predicates to include in the final set would be: 1) $implies such that
$$X/$implies/$$Y is true (ie returns a non-null set of addressed XDI
nodes) iff the symmetric difference of the set of nodes addressed by $$X and
the set of nodes addressed by $$Y is the empty set. 2) $is such that $$X/$is/$$Y is true
iff [$$X/$implies/$$Y ^ $$Y/$implies/$$X] 3) $has .. been over this one, see earlier
email with RDF analog. My take is that this (and any predicate)
should have a semantic meaning or adopters will assign their own different
meanings and things will get screwy fast. My take is also that semantic
meaning of $has is a property restriction on the class of things $$X 4) $a would imply set
membership (subClassOf for concept classes as sub and obj, rdf:type for
individual as sub and class as obj, and the implication that the class has
a single member that is the individual for a class as sub and individual
as obj) 5) $inv s.t. the set of nodes addressed
by $$X/$inv$$Y/$$Z is equivalent to the set addressed by
$$Z/$$Y/$$X.. Whether $inv$$Y or $$Y$inv is TBD AFAIK 6) binary set operators: $and, $nand,
$or, $xor, $nor, $nxor, $diff, $symdiff, $union, $intersection 7) $not .. std negation from set
membership exclusion pov While not predicates I'd also suggest the
following: $forall $forsome $prob The first two are from First Order Logic.
The last allows fuzzy logic treatment of predicates. E.g
+ball/+color$prob(0.6)/+red
+ball/+color$prob(0.2)/+green +ball/+color$prob(0.2)/$nor+green*+red The mechanisms for combining the
above (e.g. $is$a, $has$a, $is$not, etc) are and what they mean in a way
that's expressible in an RDF syntax analog warrant furthe discussion. Regards, =Bill.Barnhill From: Drummond Reed I had a very productive 1-on-1 call with Nick Nicholas after the
XRI TC telecon today, where we went into the metagraph model diagrams even more
deeply. Several key conclusions came out of it. Nick is doing his own writeup,
which may have even more detail, but in this email I wanted to highlight two key
conclusions that directly address the questions Bill raised this morning in his
message below. Also, I posted a few minor edits in a V2 of the metagraph/graph
diagrams at: http://www.oasis-open.org/committees/download.php/30719/xdi-rdf-graph-model-diagrams-v2.pdf
Note: I’m noticing how much we need to refer to the
NON-metagraph, but talking about a non-metagraph hurts my head, I propose the
term we use to talk about “the XDI RDF graph that does not include any
metagraph statements” is “base graph”, simply because
something can only be meta if it has a base to work against. Please post if you
prefer another term. ************* The first conclusion is that the V1 diagrams are, in fact, correct.
In other words, the metagraph statement +x/$has/+y does in fact translate into
two base graph statements:
+x/+y/+x+y
+x+y Both of them are reflected in the diagram: This is a different conclusion than I gave in my first response to
Bill earlier today when I said that +x/$has/+y was a way of asserting that the
target of the outgoing arc +y originating from +x was a blank node. Saying the
object is in fact +x+y is a better solution for two reasons:
1) There is no need to invoke the concept of a blank node (and all its
baggage).
2) There is no need to specify that a $has statement means there can be only
one arc +y originating from +x. Instead what +x/$has/+y describes is that:
There is an exactly one arc +y originating from +x terminating in the object
identified as +x+y. This is consistent with:
a) RDF, because there is exactly one RDF statement with the same subject,
predicate, and object (multiples of that same statement are ignored). b)
Our use of $has in the metagraph to define XDI addresses in the base graph:
$has identifies the singleton arcs in the base graph that serve this addressing
role. No more, no less. Well, actually, a little
more. There is one other
statement that can be derived from a $has statement – but it really is
just a logical conclusion that fundamentally falls out of the logical structure
of the metagraph itself. It is the following inference:
Every metagraph statement +x/$has/+y infers the statement +x+y/$is$a/+y. Kudos to Nick for recognizing this inference. The funny thing is
that it’s plain as the nose on your face if you study the metagraph/base
graph diagrams. Diagram from section 4A/4B of the PDF, which is the diagram of
the metagraph statements +x/$a/+y and +y/$is$a/+x, shows: Because both $a and $is$a statements are assertions about an object
having an incoming arc, it follows that any metagraph statement that specifies
an outgoing arc terminating in an object is also a statement that the object
has an incoming arc. Thus all four of the
following statements infer the other three:
+x/$has/+y
+y/$is$has/+x
+x+y/$is$a/+y
+y/$a/+x+y This jibes with the English semantics if we substitute real words
for x and y:
+dog/$has/+collar
+collar/$is$has/+dog
+dog+collar/$is$a/+collar
+collar/$a/+dog+collar So the English phrase “dog collar” only means that the
identified object is-a collar, not that it is-a dog. However it is not just any collar, it is-a collar in the context
of being something a dog has. This finally addresses the question Bill raised in his message
below In the RDF he provided, his assumption was that for the metagraph
statement +x+y, the RDF statements were:
1) +x+y is a +x
2) +x has the property +y. What Nick and I concluded is that the RDF statements are:
1) +x+y is a +y
2) +x has the property +y whose object is +x+y Bill, we also agreed that since you have more RDF experience than
we, it may be easier for you to express the RDF then we can. Hope this helps. =Drummond From: Barnhill, William [USA]
[mailto:barnhill_william@bah.com] Hi Drummond, I'm unclear on the
relationship between metagraph and graph. I had thought the relationship was
comparable to the relationship between the T-Box and the A-Box in
RDFS, OWL, etc. but your diagrams seem to be saying otherwise. For an example
the metagraph diagram for 2A (+x+y) leads to a graph statement of +x/+y/+x+y,
which I am having trouble relating to RDF. In my mind the XDI metagraph
statement +x+y is comparable to the metagraph statements stated in the
following RDF/XML notation: <owl:Class
rdf:about="http://plus.xri.net/x">
<rdfs:subClassOf rdf:resource="&owl;Thing" />
<rdfs:subClassOf>
<owl:Restriction>
<owl:onProperty rdf:resource=http://plus.xri.net/y
/>
<owl:minCardinality
rdf:datatype="&xsd;nonNegativeInteger">1</owl:minCardinality>
</rdfs:subClassOf> </owl:Class> Which then might
lead an XDI reasoner to entail the implicit graph statements expressed in <rdf:Description
rdf:about="http://equals.xri.net/Bill.Barnhill" >
<rdf:type rdf:resource="http://plus.xri.net/x" /> </rdfDescription> from the explicit
graph statements expressed in: <rdf:Description
rdf:about="http://equals.xri.net/Bill.Barnhill" >
<rdf:type rdf:resource="&owl;Thing" />
<plus:y>!1234!234</plus:y> </rdfDescription> In XRI
terms the following implicit XRI in the XDI graph would be determined
by an XDI reasoner: =Bill.Barnhill/$a/+x from the following
explicit XRIs in the graph (playing fast and loose with name spaces here): =Bill.Barnhill/$a/+Thing =Bill.Barnhill/+y/!1234!234 and a query on the
graph of $$X/$a/+x will answer [{"$$X", "=Bill.Barnhill"}] Could you explain
how the above would be done with the metagraph predicate framework described by
your diagram and recent wiki update? Regards, =Bill.Barnhill From: Drummond Reed Following is the agenda for the unofficial telecon of the XDI TC at:
Date: Thursday, 15 January 2009 USA Time: 1:00PM - 2:00PM Pacific Time (21:00-22:00 UTC)
TO ACCESS THE AUDIO CONFERENCE: Dial In Number: 571-434-5750 Conference ID: 5474
AGENDA
1) XDI ADDRESSER
We will start with a tour from Markus of his latest XDI RDF utility:
http://graceland.parityinc.net/xdi-addresser/XDIAddresser
2) SOLVING THE RUBIK'S CUBE OF THE XDI 1.0 RDF METAGRAPH MODEL
Based on insights from Monday's aborted XRI/XDI editor's telecon (which turned into a long informal XDI telecon) and Tuesday's special XRI Syntax 3.0 telecon (which also ended out as a long XDI discussion), Drummond had a key revelation about the metagraph model.
He has uploaded a PDF with a new set of diagrams illustrating the metagraph model and how it describes the graph model.
http://www.oasis-open.org/committees/download.php/30700/xdi-rdf-graph-model- diagrams-v1.pdf
He also updated the XDI RDF Graph Model wiki page with new text descriptions of each metagraph predicate and references to the diagrams.
http://wiki.oasis-open.org/xdi/XdiOne/RdfGraphModel
The main topic of the call will be to review this and discuss how it returns the metagraph back to a pure description of the graph with no other semantics and thus enables the metagraph predicates to be used with any description logic:
http://en.wikipedia.org/wiki/Description_logic
3) MULTI-PART SPEC DESIGN AND NEXT STEPS WITH THE FIRST WORKING DRAFT
Drummond had his questions answered by Mary McRae about how a multi-part specification should work. See the DITA example:
http://docs.oasis-open.org/dita/v1.1/OS/overview/overview.html
Given this model, Drummond has updated the specification names on:
http://wiki.oasis-open.org/xdi/XdiOneSpecs
If there is consensus on this, our next step is to choose a template and begin the first Working Draft.
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