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Subject: Minutes: XDI TC Telecon Thursday 1-2PM PT 2009-12-15
Following are the minutes of the unofficial telecon of the XDI TC at:
Date: Thursday, 15 December 2009 USA
Time: 1:00PM - 2:00PM Pacific Time (21:00-22:00 UTC)
1) XDI RDF BOX GRAPHING
Drummond posted a PDF file of a new version of the XDI RDF box graphing document with much more detail:
We reviewed it and the following suggestions were made:
a) Change "XDI Statement" to "XDI Address" in the titles
b) Add a note about literals and XDI addresses.
On the second point, we were reminded that we have never fully closed on the question of literals and XDI addresses. Markus reminded us that there was a proposal that there be a full XRI version of X3 where literals were encoded as XRIs, and the XDI4J library's XDI Converter currently supports this.
#ACTION: Drummond to add this to the 2010 agenda items.
2) $HAS SEMANTICS AND ASSOCIATIVITY
The box graphing discussion then led us back to the topic that brought it up, which was Giovanni's raising of an issue with the current link contract examples where the semantics does not appear correct.
We focused on associativity of $has as an "operator". Giovanni pointed out that it could be "associative" or "non-associative", and if associative, it could be "left associative" or "right associative". The definitions we were referencing were from two different pages on Wikipedia:
We agreed that the XDI statement:
+a+b INFERS +a+b/$is$a/+b
Giovanni's question was then whether
a+b+c INFERS +a+b+c/$is$a/+c OR +a+b+c/$is$a/+b+c
Drummond's answer was that it infers both. In English:
house door keyhole
A house door keyhole IS A keyhole AND
A house door keyhole IS A door keyhole
A car door keyhole is a door keyhole but NOT a house door keyhole
We then talked about the link contract example:
Giovanni pointed out that the semantics are wrong because:
$contract=markus DOES NOT INFER $contract=markus/$is$a/=markus
He felt that this was not correct semantics, and that this was a problem since XDI semantics should be mathematically expressable so it can be used as a reasoning language.
Drummond agreed on both counts. He felt the example should be revised to:
This shows how $has remains "left associative" and how cross-references can be used so that every $is$a statement inferred by a $has statement is true, enabling semantic correctness.
Drummond noted that even though $has operations are left associative, they are not commutative, i.e., you cannot change the ORDER of any subsegments in the sequence.
#ACTION: Giovanni to confirm the correct associativity term on the Wikipedia pages.
(Post-meeting note: This is DONE – Giovanni sent an email to the
list confirming that the correct term is that $has is "left
associative", meaning that in the absence of parentheses (cross-references),
the $has "operator" should be processed from left to right.
3) NEXT MEETING
The members agreed to take a holiday break. The next XDI TC telecon will be Thursday January 7 2010.