A new observation about $ref/$rep behavior

[Markus Sabadello <markus.sabadello@xdi.org>]

In working on the XDI2 Facebook connector, I came across some interesting behavior of $ref/$rep equivalence links.
Warning, this is a pretty advanced application of the equivalence links concept and probably not so easy to read.

Let's say my "e-mail address in my Facebook account" is expressed as follows:

(https://facebook.com/)[!]!588183713+(user)<+(email)>&/&/"markus.sabadello@gmail.com"

Note that 588183713 is my Facebook user ID.

Now I want my Facebook data to be accessible to XDI clients that only know my Cloud Number, but not my Facebook user ID.

Let's say my Cloud Number is [=]!1111. So I create the following $ref link:

(https://facebook.com/)[=]!1111/$ref/(https://facebook.com/)[!]!588183713

Thanks to this new $ref link, my "e-mail address in my Facebook account" can now be accessed via either one of the following XDI addresses:

(https://facebook.com/)[!]!588183713+(user)<+(email)>
(https://facebook.com/)[=]!1111+(user)<+(email)>

Now I want to go one step further and create a $ref link from my "primary e-mail address" to my "e-mail address in my Facebook account":

[=]!1111<+email>/$ref/(https://facebook.com/)[=]!1111+(user)<+(email)>

So I end up with the following graph:

(https://facebook.com/)[!]!588183713+(user)<+(email)>&/&/"markus.sabadello@gmail.com"
(https://facebook.com/)[=]!1111/$ref/(https://facebook.com/)[!]!588183713
[=]!1111<+email>/$ref/(https://facebook.com/)[=]!1111+(user)<+(email)>

Looks nice, but it is actually invalid, since the context node (https://facebook.com/)[=]!1111 now contains both a $ref relation and a sub-context.

Instead, it would have to be this:

(https://facebook.com/)[!]!588183713+(user)<+(email)>&/&/"markus.sabadello@gmail.com"
(https://facebook.com/)[=]!1111/$ref/(https://facebook.com/)[!]!588183713
[=]!1111<+email>/$ref/(https://facebook.com/)[!]!588183713+(user)<+(email)>

The primary goal of this whole exercise has thus been achieved, which is to make my "e-mail address in my Facebook account" accessible via the following XDI address:

[=]!1111<+email>

However, the weakness is that the $ref that links my Cloud Number to my Facebook user ID is not being used. So if for some reason my Facebook user ID changed, I would have to update potentially a large number $ref links all over the place, rather than having a single $ref link that controls the "Cloud Number to Facebook user ID" mapping.

Not a big problem for now, but a bit unsatisfying.

Markus

P.S. I remember we said that my Facebook user ID should be represented as [=]!588183713 instead of [!]!588183713, but this doesn't change anything about the above observation.