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Subject: Minutes: XDI TC Telecon Thursday 1-2PM PT 2009-02-05
Following are the minutes of the unofficial telecon of the XDI TC at: Date: Thursday, 05 February 2009 USA Time: 1:00PM - 2:00PM Pacific Time (21:00-22:00 UTC) ATTENDING Markus Sabadello Giovanni Bartolomeo John Bradley Drummond Reed Bill Barnhill AGENDA 1) CONFERENCE CHAT ROOM Thanks to Bill Barnhill, we are now able to use an XMPP chat room, from which we will copy comments into the minutes. See the instructions from Bill at: http://lists.oasis-open.org/archives/xdi/200902/msg00010.html 2) GENERAL UPDATES Drummond explained that since his absence at a funeral last week, he is a week behind. He is currently aiming to have the XRI 3.0 Syntax draft by Feb. 19, so the first Working Draft of the XDI 1.0 Addressing and RDF Graph Model may not be until the end of the month. 3) UPDATE ON $HAS SEMANTICS The balance of the call was spent discussing points in Drummond's message posted here... http://lists.oasis-open.org/archives/xdi/200902/msg00005.html ...in addition to some of Giovanni's and Markus's questions posted here: http://lists.oasis-open.org/archives/xdi/200902/msg00001.html ...and some of Nick's questions posted here: http://lists.oasis-open.org/archives/xdi/200902/msg00000.html We looked at the set of statements that Drummond and Markus concluded are reflected by the XDI subject +x+y: #1) +x/$has/+y #2) +y/$is$has/+x ;inverse of #1 #3) +x/+y/+x+y #4) +x+y/$is+y/+x ;inverse of #3 #5) +y/$a/+x+y #6) +x+y/$is$a/+y ;inverse of #5 #7) +x/$has$a/+y #8) +y/$is$has$a/+x ;inverse of #7 Bill asked to clarify the semantics of $is. Drummond explained that it is the self-referential arc, which means that by itself it is the logical equivalence predicate, i.e., owl:sameAs. As a prefix for other XRIs, it is the inversion predicate. Giovanni noted that his graph approach is to draw $is statements as multiple subject arcs from the context root to the same node. He also warned not to mix his graph notation with that we have used on other posts to the list as his starts from a different assumption about semantics of graph nodes and arcs. Markus pointed out the logical equivalence of $is statements is not necessarily reflected by the appearance of some serialization formats like X3, however there does not appear to be any logical conflict. He wants to think through the implication that if +x/$is/+y, a $get on +x is effectively a $get on + y too if +y is present in the same graph. Bill said this is the same as treating each XRI is a subgraph, and a $is statement combines two XRI subgraphs into a new (logical union) subgraph. We returned to the +x+y discussion and statement #6, +x+y/$is$a/+y. Nick pointed out that some compound XRIs in the XDI RDF Model doc don't seem like are "is a" statements about the final XRI subsegment. An example was $uri$http -- it should probably be $http$uri. Drummond noted that hierarchical classification (specialization) commonly works from general to specific, and this should be able to be done with $has statements too. But Nick is right - the way this works has important implications for discoverability. Nick also noted the typical "individual/class" distinction between $has and $has$a. For example, =abraham/$has$a/+wife and =abraham/$has/=sarah. Note however that there is also a valid use case for the statement =abraham/$has/+wife. It lets you describe the XDI subject =abraham+wife ("the wife of Abraham), e.g., =abraham+wife/$is/=sarah. Whether there is any valid use case for =abraham/$has$a/=sarah remains to be seen. Drummond and Markus worked out the RDF for $has relationships and arrived at the same conclusion as Bill. The XDI RDF subject +x+y would be expressed as the following three RDF statements: A) <xri:+x+y> <rdfs:subClassOf> <xri:+y> B) <xri:+x+y> <xri:$is+y> <xri:+x> C) <xri:$is+y> <rdfs:inverseOf> <xri:+y> Bill asked, if +x/$has/+y and @example$1/$a/+x implies that @example$1+y, right? # DRUMMOND to Drummond has the AI to think about Bill's question. # BILL to send a reference about classification to the list. Bill provided the following reference on tableau reasoning: http://www.idi.ntnu.no/emner/tdt44/handouts/Ontology%20Reasoning%20%20V2008. pdf Giovanni asked "Is #3 above, i.e., +x/+y/+x+y, really an inference from +x+y? He suspect this is biased from a specific notation. However since we ran out of time, Drummond suggested we take that question to the list.