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Subject: Re: [xdi] Two terminology questions: "global" and "root"

Yes this is a great summary of the two approaches.

I still don't see where exactly the semantic interoperability would come from, but I do understand the reasoning behind the "global root" / authority-relative approach.


On Thu, Nov 28, 2013 at 12:08 AM, Drummond Reed <drummond.reed@xdi.org> wrote:
On Wed, Nov 27, 2013 at 2:26 PM, Markus Sabadello <markus.sabadello@xdi.org> wrote:
Right now I still like "local root" better than "outer root" or "global root", but in case I get more comfortable with your views about all roots being shared, then I think I will also like "global root" more :)

That really does go to the essence of the whole graph merge issue: are all top-level XDI graph roots local or global? Here's the way I analyze it:

If all top-level XDI graph roots are local, then it means that all XDI statements in those graphs are relative to that particular graph. That means the truth of a statement must always be evaluated relative to the graph in which it appears.

If all top-level XDI graph roots are global, then it means that all XDI statements in those graphs are not graph-relative. They apply globally, i.e., the truth of a statement is not relative to or dependent on the graph in which it appears. Anyone can assert anything about anyone, but they must make that statement under their own authority, and if that statement is shared with another target XDI graph, the statement should be identical in that target graph, so the same statement is relative to the same authority in all XDI graphs.

And if there is ever a question about the fidelity of an XDI statement, i.e., is it an exact copy of the authoritative statement in the authoritative XDI graph, the process for verifying its fidelity is always the same: resolve the authority to the authoritative graph, and verify the original statement there. If there is a conflict, the non-authoritative copy of the statement is in error and should be corrected.

The reason I'm so passionate about the latter is that it is the only way I believe XDI semantics can be interoperable across all XDI graphs. Without fidelity of XDI statements across graphs, we won't have semantic interoperability.

And that is the reason that I now favor adopting the term "global", because it suggests that the top-level root of all XDI graphs is shared among all peer graphs. The only other option I see is "common root" or "shared root".



On Wed, Nov 27, 2013 at 4:35 PM, Drummond Reed <drummond.reed@xdi.org> wrote:
On Tue, Nov 26, 2013 at 8:06 AM, Joseph Boyle <planetwork@josephboyle.net> wrote:
“Global” would be clear than “outer”.

In reference to Joseph's suggestion above, we adopted the term "outer graph" for these reasons:
  1. It fit naturally along with "inner graph", a term which we have used from the start.
  2. The term "local" seemed to miss the idea that the outer root is shared by all XDI graphs.
  3. We were wary of using the concept of "global" since it suggests a global root.
  4. We haven't come up with anything better. 
However what I have found in practice is that the term "outer graph" is just not intuitive the way "inner graph' is. So I agree we need a better term.

Secondly, I agree with Joseph that the term that always naturally comes to mind is "global graph" since it communicates that all XDI graph instances are part of a logical global graph.

My only reticence around "global" is #3 above—that it suggests a global root. Which brings me to question #2:

In my discussions on the list and with Markus about the graph merge issue, I have suggested that we should avoid the term "root" because it suggests that XDI architecture is hierarchical in the same way as conventional directory architecture.

However Markus pointed out that since XDI contexts are indeed hierarchical, the term "root" does make sense from that perspective. And in practice is the term that naturally comes to mind.

So here is the suggestion I want to float for feedback from all TC members:
  1. Switch from using "outer graph" to "global graph".
  2. Use the term "root" or "root node" when talking about the starting node of a global, peer, or inner graph, but emphasize the fundamental heterarchical structure of the XDI graph model, i.e., that all XDI peer graphs are peers within the XDI global graph, and every peer graph shares the same global root  node as every other peer graph.
(Note that inner graphs are different from peer graphs in one crucial way: even though an inner graph root restarts XDI addressing just like a global root or peer root, the nodes in the inner graph cannot be addressed outside of the context of the containing XDI graph. So the inner graph is "dependent" on the containing XDI graph.)

Please post your thoughts as to whether you agree or disagree with these terminology suggestions.


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