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Subject: RE: [xdi] Minutes: XDI TC Telecon Thursday 1-2PM PT 2009-04-02
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Bill, I haven’t had time to read through
the whole page you referenced here (http://c2.com/cgi/wiki?ConceptOrientedModel), but what I did have time to read looked very interesting. I would definitely encourage you to create
a separate wiki page about it. After RSA I should have more time to read
through and get further into this. =Drummond From: Barnhill,
William [USA] [mailto:barnhill_william@bah.com] Sounds like an interesting discussion. Do you think the following
attributes of my 'subjects as communities' proposal might help: .. Every XDI subject or predicate is a community .. for subjects rooted in @ global
context this is obvious .. for subjects rooted in + global
context the community is the set of objects that are instances of that concept .. I
found similarities between + words and Concept Oriented Model (http://c2.com/cgi/wiki?ConceptOrientedModel) .. for subjects rooted in = the community
consists either of all versions of that individual, or of the most current
version (a community of one) .. for xrefs the community definition is
completely dictionary dependent .. A community of the form (s/p) is the community that is the
subset of the p community where every member of the subset has a relationship
with one or more members of the members of s. The details of this relationship
are TBD topic of further discussion along lines of $has details, but
I view it as similar to the 'IN' concept in Concept Oriented Model and view
whether it's aggregation or composition as defined by the XDI dictionary
description of p. That we're using XRIs to express the relationship I think
gets around http://c2.com/cgi/wiki?LimitsOfHierarchies. .. So a statement of the form s/p/o then would be stating
that o is a member of (s/p)
The concept above of 'subjects as communities' is modified to include
the s/p discussions we've had on the list. I need to flesh this out more and put it onto the wiki for comments.
Should I add it to the metadata page Giovanni created, or should I make
it a separate page? I'm leaning towards a separate page. Thanks, Bill From: Drummond
Reed Following are the minutes of the unofficial telecon
of the XDI TC at: Date: Thursday, 26 March 2009 USA Time: 1:00PM - 2:00PM Pacific Time ATTENDING Giovanni Bartolomeo Markus Sabadello Nick Nicholas Drummond Reed John Bradley 1) CONTINUE $HAS AND $HAS$A DISCUSSIONS Our main topic was discussion the open issues dialog
at the bottom of:
http://wiki.oasis-open.org/xdi/XdiMetamodel Giovanni started with the statement inferred by =abraham/$has/+son,
which is =abraham+son/=isaac/=abraham+son=isaac. His first concern is that from
an RDF standpoint, the semantics may not be clear. His second concern is that
they may conflict with the semantics of the original RDF document. RE the first concern, we discussed what it means
that =isaac appears as a predicate in the statement
=abraham+son/=isaac/=abraham+son=isaac. Drummond pointed out that this is a
valid RDF statement, however it is not the type of statement for which RDF
properties are typically used. Giovanni said that the problem is that =isaac is an
instance, and you can't use an instance as a property. Drummond pointed out
that it is common in XDI RDF for a subject to also be a predicate, in fact that
is the entire premise of XDI RDF dictionaries: every predicate appears in the
dictionary as a subject. He used the example of +email as a subject, predicate
and object:
+email/$is$a/$a$xsd$string =drummond/+email
=drummond/+email/(=drummond+home/+email)
=drummond/+email/(=drummond+work/+email)
=drummond/$has$a/+email Nick gave the example of putting a person in
context, for example, placing =drummond in two different contexts:
@cordance=drummond and @oasis=drummond. The $has statement for the first is @cordance/$has/=drummond This infers the statement
@cordance/=drummond/@cordance=drummond Here is a good example of where =drummond (typically
looked at as an “instance”) has a clear use as a predicate identify
a specific context for =drummond. Giovanni then gave two specific examples: =abraham/+son/=isaac
=abraham/+son/=abraham+son He said that in the first case, the range of +son
would be instances of the class +son. Whereas in the second case, the range is
another class – a specialization of +son. Giovanni pointed out that in the first case the
object is an instance of the range of the predicate, but not in the second
case. So the second case is an exception to the normal behaviour in RDF. Drummond pointed out that this is the fundamental
“extension point” for all of XDI RDF. $has statements are the way
of creating all the classes and instances that exist, and the addresses for
those classes and instances. He said this is similar to the concept of defining
new names in any language, such as English. For example, “A plane made by
Boeing is called a Boeing plane.” That’s how you create the new
concept, “Boeing plane”. RDF does not have such a concept because, to our
knowledge, there are not RDF statements that create new URIs. URIs are opaque
in RDF. So when i XDI RDF the statement =abraham/$has/+son asserts a
relationship of two identifiers that results in a third identifier, we have
stepped outside of the semantics that can conventionally be expressed in RDF. Drummond wondered whether the way to make this
compatible with RDF to propose that there is an algorithmic way to extend RDF
ranges in XDI RDF, and it is built into all XDI RDF range types. This
“range extension algorithm” would be defined as: “Any XRI that
is a concatenation of XRI A with XRI B is an extension of the range of XRI
B.” This would meet the goal Giovanni suggests of
keeping XDI RDF as close to original RDF as possible, without taking away the
power of XDI RDF addressing. We closed by Giovanni saying he would like to
propose a different solution for how XDI RDF addressing could work, which will
will make the subject of next week's call (and discussion on the list this week
if there is time). # ACTION: GIOVANNI to write up his proposed
alternative for XDI RDF addressing. |
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