XDI Metamodel wiki page (was Minutes: XDI TC Telecon Thursday 1-2PM PT 2009-03-19)

["Drummond Reed" <drummond.reed@cordance.net>]

Giovanni,

Yes, I strongly agree that we should start to focus all our discussions
about the XDI RDF metamodel on the wiki page you created, since it is much
easier to track discussions as we have them (email, telecons, offline, etc.)
and note conclusions there so we have them in one place.

I would also suggest that we create an "issues list" at the bottom of the
page where each aspect of the metamodel where we believe we have an
unresolved issue is listed. Then we can use that issues list to drive our
discussions towards the consensus we need to put out the first draft of the
XDI Addressing and RDF Graph Model spec.

Thanks,

=Drummond 

> -----Original Message-----
> From: Giovanni Bartolomeo [mailto:giovanni.bartolomeo@uniroma2.it]
> Sent: Sunday, March 22, 2009 11:16 AM
> To: Nick Nicholas; Barnhill, William [USA]; Drummond Reed
> Cc: 'OASIS - XDI TC'
> Subject: Re: [xdi] Minutes: XDI TC Telecon Thursday 1-2PM PT 2009-03-19
> 
> Dear Drummond,
> 
> thanks for the minutes. Please let me point out once more that what
> discussed refers to the wiki page
> 
> 	[6] http://wiki.oasis-open.org/xdi/XdiMetamodel
> 
> which represents just a first attempt to summarize the discussion we
> have had during last weeks. In particular, I would like to ask Nick
> and Bill to please review that page and check whether I've properly
> understood their points, or correct what they think is not properly
> reported. I would like to propose to use this page to track the
> evolution of this debate.
> 
> Thanks,
> Giovanni
> 
> At 07.29 20/03/2009, Drummond Reed wrote:
> Following are the minutes of the unofficial telecon of the XDI TC at:
> 
> Date:  Thursday, 19 March 2009 USA
> Time:  1:00PM - 2:00PM Pacific Time (21:00-22:00 UTC)
> 
> ATTENDING
> John Bradley
> Giovanni Bartolomeo
> Markus Sabadello
> Drummond Reed
> 
> REGRETS
> Bill Barnhill
> Nick Nicholas
> 
> 
> 
> 1) CONTINUE $HAS AND +X/+Y/+X+Y DISCUSSIONS
> 
> See the minutes of the second-to-last last meeting at:
> 
> 	[1] http://lists.oasis-open.org/archives/xdi/200903/msg00005.html
> 
> Also the most recent posts at:
> 
> 	[2] http://lists.oasis-open.org/archives/xdi/200903/msg00004.html
> 	[3] http://lists.oasis-open.org/archives/xdi/200903/msg00006.html
> 	[4] http://lists.oasis-open.org/archives/xdi/200903/msg00007.html
> 	[5] http://lists.oasis-open.org/archives/xdi/200903/msg00008.html
> 
> We continued the discussion by reviewing the new wiki page posted by
> Giovanni:
> 
> 	[6] http://wiki.oasis-open.org/xdi/XdiMetamodel
> 
> 
> Giovanni started by saying that =abraham/+son/=isaac belongs to the
> class/instance level. By contrast the metagraph statement
> =abraham/$has/+son
> describes that an arc labelled +son is drawn from the node =abraham.
> 
> He explained tha tif two terms are subject and object of a statement
> containing the predicate $has, then a new node is introduced in the graph,
> whose identifier is the composition of the subject's identifier and the
> object's identifier. In this case, the new introduced node is =abraham+son
> 
> He noted that =abraham+son is a node, whereas =abraham/+son identifies the
> set of nodes which are the objects of the predicate =abraham/+son (as
> described in XDI/RDF v12).
> 
> However, =abraham/$has/+son does not tell anything about the relation
> between =abraham and +son. To specify that this relation is actually an
> aggretion, the predicate $has$a is used: =abraham/$has$a/+son. $has$a
> gives
> you more information than $has. It says that the outgoing arc is related
> to
> the node in a aggregation relationship.
> 
> Giovanni proposed that one way to interpret this is that $has could
> specialize into $has$a, $a, $is$a, and others. Drummond noted that the
> only
> issue here is that the other metagraph predicates do not necessarily imply
> a
> $has arc - $has has its own particular specialization (addressing).
> 
> Giovanni said another rule is that every XDI/RDF predicate (either in the
> model or in the meta-model) defines, in the metamodel, the group of its
> own
> objects. For example, with regard to =abraham/+son/=isaac, which infers
> +son/$a/=isaac, tells that the group +son, has =isaac among its members.
> 
> Giovanni suggests that the terms "group" and "member" are more accurate in
> the metalevel than "class" and "instance" or "individual" when it comes to
> XDI RDF.
> 
> Giovanni it is possible to further identify which subgroup =isaac is
> member
> of =abraham+son/$a/=isaac tells that the group =abraham+son, has =isaac
> among its members (the only new thing here is the terminology).
> 
> Giovanni next said $a is a special case of $has. He concludes that having
> assigned the metaword $has the semantics of describing the connection
> between a node and any generic outgoing arc the node may own, a statement
> like =abraham+son/$has/=isaac and an identifier like =abraham+son=isaac do
> not describe anything about the relationship between =abraham+son and
> =isaac, apart that they are connected through an arc.
> 
> Drummond said he wants to explore this further because of the inherent
> predicate semantics of any RDF arc, i.e., do all RDF arcs represent XDI
> RDF
> $is$a statements. This is an open issue.
> 
> Giovanni said =abraham+son=isaac describes =isaac in the context of
> =abhrahm+son. This asserts that =abraham+son/$a/=isaac (of which the
> inverse
> is =isaac/$is$a/=abraham+son). If $is$a is also a special case of $has,
> that
> would mean =isaac/$has/=abraham+son.
> 
> Drummond said that the relationship between the two statements is that
> =abraham+son/$has/=isaac infers that =abraham+son/$a/=isaac, but the
> inverse
> relationship between the two statements is not required to be true.
> 
> Giovanni said Nick suggested $is$a could be a special case of $has like
> $has$a is a special case of $has. Drummond believes it is the other way
> around: $has is actually a special case of $has$a. That's why
> =abraham+son/$a/=isaac and  =abraham+son/$has/=isaac are different
> statements. The first expresses a subtyping relationship. The second
> expresses an addressing relationship that, by our earlier discussions,
> _also_ represents a subtyping relationship. So we could say that a $has
> relationship infers a $a relationship, but a $a relationship does not
> infer
> a $has relationship.
> 
> Giovanni said $has could be generic (Nick calls it "vague") and could be
> used to describe the relationship between nodes linked by any other $
> predicates. Drummond said $has actually creates a very specific type of
> relationship between two nodes: an addressing arc, the concept of which is
> not part of standard RDF.
> 
> John said that =abraham/$has/+son creates a class (what Giovanni calles a
> "group") representing an aggregation, and =abraham+son/$has$a/=isaac
> assigns
> an instance to that aggregation. So $has is about classes and $has$a is
> about instances.
> 
> Drummond said that $has has one "specific" thing about it, which is that
> it
> create the addressing relationship between the nodes.
> 
> Giovanni said that he thought that was true, but in reading Nick's email
> he
> realized something different.
> 
> Unfortunately at that point we ran out of time, so we will try to continue
> this discussion on the list, or worst case next week's telecon (provided
> Giovanni can make it).
> 
> 
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