[sugar] Datastore id vs. Activity instance id

[Eben Eliason]

> I don't think having a strict one-to-one relation between datastore
> ids and activity ids is a good idea. If I am working in one activity,
> maybe writing some text, and then want to start a new one - why would
> I be forced to quit the current activity and start a second instance?
> Not only is this highly inefficient but also inconvenient. Why can't
> I just "switch" this activity instance to the new datastore object?
> Same for something like "keep-as", where you fork off work on branch
> - simplest would be just creating a new object in the DS.
>
> Btw, the current datastore API allows this just fine.

Actually, the point of the bug is mostly in keeping with what you're
saying.  The problem currently is that "opening" the same document in
the Journal can result in two separate running instances.  This is
inconsistent with our goals and also with most systems in general,
which simply focus the already opened instance.

I will say that I don't agree with the idea of "swapping" the ds_id
within an open activity instance.  In our metaphor, this would be like
opening document B inside the *window* that used to contain document
A; This should not happen, and is not what would happen on most
systems now -- you'd simply have two open windows within the
application.  On the other hand, I do think the "keep-as" scenario you
mention is a valid exception.  This - just like on modern systems -
does generally change the ds_id of the  object inside the current
window, or in our case, activity instance.