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Subject: RE: [xdi] Minutes: XDI TC Telecon Thursday 1-2PM PT 2010-01-07
Hi Drummond,
I have to agree with Giovanni's comments.
You said "...
In other words, +a/$has/+b does NOT imply +a/+b. Instead +a/$has/+b implies (+a/+b).
..." As I understand it we have agreed on a correspondance between $has and rdf:property with minCardinality of 1. If Class A has property B with minCardinality of 1 and resource #1 in the graph is a A then it MUST follow
that there is a statement asserting the property value for property B of resource C. Putting in XRI terms and marking statements:
(1) If Class A has property B with minCardinality of 1 [+A/$has/+B]
(2) and resource #1 in the graph is a A [$1/$is$a/+A]
(3) then it MUST follow by def of minCardinality that there is a statement asserting the property value for property B of resource C [$1/+B].
(4) Since this holds true for all $1 that are +A
(5) (the set of nodes that can replace $1 and have this be true is the same as the set of nodes represented by +A)
(6) then the graph must assert [+A/+B].
(7) If a graph asserts statement S then by definition it is saying something about S therefore it also must assert (S)
(8) Because of (7) and (6) the graph must assert (+A/+B)
To sum up, unless one of the above statements is incorrect I cannot see a way for any of the following three statements not to imply the other two (ie they are logically equivalent):
(+A/+B) <=> +A/+B <=> +A/$has/+B
You also said again "...
The parentheses, for reification, are absolutely necessary or XDI semantics falls apart.
..."
I agree that parenthesis are necessary and that they represent reification. Not sure XDI semantics would fall apart without that but definitely the more interesting bits to me of the semantics would. That said I
still don't understand why that means the reasoning above is not correct. I suspect the issue is in $has necessitating a minCardinality of 1.
Kind regards,
Bill Barnhill
Booz Allen Hamilton - Rome, NY
315-330-7386 | william.barnhill.ctr@rl.af.mil |
barnhill_william@bah.com
From: drummond.reed@gmail.com [drummond.reed@gmail.com] On Behalf Of Drummond Reed [drummond.reed@xdi.org] Sent: Wednesday, January 13, 2010 4:04 AM To: Giovanni Bartolomeo Cc: OASIS - XDI TC Subject: Re: [xdi] Minutes: XDI TC Telecon Thursday 1-2PM PT 2010-01-07 Giovanni,
I apologize for any misunderstandings - in my attempts to take notes about what are often long discussions on our calls (in which I am an active participant), I am not always able to faithfully capture exactly what was said. I try to do it afterwards, but I am sure I make mistakes. What makes it even harder is that sometimes we discuss and appear to reach agreement on a certain topic, only to later realize (sometimes hours later, sometimes days later, sometimes weeks later) that there are problems with our solution, and that we need to change something. Some of the references you provide below are examples. We reached a number of conclusions last spring that, to my understanding, we later realized there were problems. I highlight one of those in particular inline below. Look for [=Drummond] On Wed, Jan 13, 2010 at 12:21 AM, Giovanni Bartolomeo
<giovanni.bartolomeo@uniroma2.it> wrote:
Dear Drummond, [=Drummond] While it is correct that Bill said that in the last call, I pointed out immediately after he said it that this was not the agreement that the TC had reached last spring (at least as I understood and documented it in the wiki spec page). In other words, +a/$has/+b does NOT imply +a/+b. Instead +a/$has/+b implies (+a/+b). The parentheses, for reification, are absolutely necessary or XDI semantics falls apart. We captured this intent in the wiki spec page where we say: "When used alone as a metagraph predicate, $has is an assertion that reifies this subject/predicate relationship so that this reification can serve as a new XDI RDF subject node." (However I believe that our discussions over the last month prove that we must provide much more detail in the spec about $has relationships. So this is an action item for all of us.)
[=Drummond] Again, the problem here is that what I wrote in that message (dated April 30 2009) was what I believed at the time, but that was only a discussion thread, not a final TC decision. What we later decided (again, this is my understanding) was that there was a mistake in the above examples, because the final statement in each set of examples need to be REIFIED (i.e., in parentheses). In other words, +x/$has/+y INFERS (+x/+y) INFERS +x+y By contrast, +x/$has$a/+y INFERS +x/+y (notice, no parentheses) Again, this is both my current understanding, and what we documented in the wiki spec at http://wiki.oasis-open.org/xdi/XdiOne/RdfGraphModel. See the examples (in yellow) listed in the * $has and $is$has * $has$a and $is$has$a sections. In particular, the example in the $has and $is$has section says: +x/$has/+y ==> (+x/+y) ==> +x+y |
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