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Subject: Minutes: XDI TC Telecon Thursday 1-2PM PT 2009-05-07
Following are the minutes of the unofficial telecon of the XDI TC at: Date: Thursday, 07 May 2009 USA Time: 1:00PM - 2:00PM Pacific Time (20:00-21:00 UTC) ATTENDING Markus Sabadello Giovanni Bartolomeo Drummond Reed John Bradley REGRETS Bill Barnhill AGENDA 1) REVISED $HAS AND $HAS$A DEFINITIONS We continued to discuss the new proposed definitions for these metagraph predicates. See the following list messages for background: http://lists.oasis-open.org/archives/xdi/200905/msg00004.html http://lists.oasis-open.org/archives/xdi/200905/msg00005.html http://lists.oasis-open.org/archives/xdi/200905/msg00009.html We began by discussing Drummond's last post (the last link above). Drummond explained that the distinction between $has and $has$a was particularly useful in XDI dictionary definitions because it allowed the dictionary author to explicitly declare: 1) When a dictionary subject is related to another dictionary subject in a way that creates a new dictionary subject ($has). 2) When a dictionary subject has a property ($has$a). For example: +car $has +tire +hood +horn $has$a +age +serial+number +color The first set of $has dictionary statements produces the new dictionary subjects: +car+tire +car+hood +car+horn By contrast, the $has$a statements simply indicate that it +age, +serial+number, and +color are all valid properties of +car. Giovanni asked if the same subject could the object of both a $has and a $has$a statement from another subject. For example: +car $has +horn $has$a +horn Drummond agreed it could. The difference between the $has and $has$a statements is that the $has statement is an assertion that there exists another XDI RDF subject that serves to identify the new set, whereas the +x/$has$a/+y statement does NOT assert that there exists another XDI RDF subject that identifies the new set, is only asserts that the property +y is a valid property on +x. Giovanni felt that for any property +y on a subject +x, there may be the need to talk about the set of objects that have that property on that subject, and that implies +x+y (+x/$has/+y). Drummond agreed that this implication can always be made, and thus an XDI context that had an instance of +x/+y/... could always be queried about +x+y. However that doesn't solve the use case where you just want to query +x to find out: a) what subsets it has, and b) what properties it has. $has and $has$a satisfy these use cases because you can do the query: [subject-making-query] $get / +x $has $has$a It was agreed to continue discussion on the mailing list.
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