Ordering

I reviewed how ordering currently works in XDI.

As we know, statements are inherently unordered, but order can be introduced through additional statements.

I think the idea is that we want to be able to #1 order members in a collection, and #2 order relational arcs on a context node.

Both is relevant for messaging, as described here:

https://wiki.oasis-open.org/xdi/XdiMessagePatterns#StatementOrderingRules

#1 is used for ordering messages in a message envelope

#2 is used for ordering operations in a message

#1 I think is pretty well specified here:

https://wiki.oasis-open.org/xdi/XdiMultiplicity#Ordering

You can try it here:

http://xdi2.projectdanube.org/XDILocalMessenger?category=6&sample=1

When looking at #2, I ran into a question:

#2.A. Do we want to be able to order relational arcs of the same type? I.e. do something like this:

=markus/+friend$*1/=joseph

=markus/+friend$*2/=animesh

=markus/+friend$*3/=drummond

#2.B. Or do we want to be able to order all relational arcs, independent of the type. This would be what we'd need for messaging, i.e.:

.../$add$*1/...

.../$del$*2/...

.../$mod$*3/...

You can try it here:

http://xdi2.projectdanube.org/XDILocalMessenger?category=6&sample=2

So I think #2.B. is what we want, but maybe anyone has thoughts on this.

BTW I think XdiOrdering should be its own proposal, with both XdiMultiplicity and XdiMessagePatterns referencing it.

Also, in a few places on the wiki, $is is used for ordering, but it should be $ref. I can make these changes.

Markus