[model] Why Motivations cannot be on Bodies

Apologies in advance as this likely reads as lecturing, but there's a lot
of background that needs to be understood (or at least accepted) to explain
why motivations cannot be directly associated with bodies.

Linked Data and RDF assume a globally scoped, open world model, in which
anyone can make any assertion about any resource, and the context of that
assertion is not at all relevant.  Thus if I make the assertion that a
photo depicts Paris, and someone else makes an assertion that the same
photo depicts Tokyo (they both have big towers after all), that's
completely acceptable.  If this wasn't the case, then there would be
semantic battles in the same way as wikipedia has edit wars, but in a fully
distributed system.  Further, if something is not asserted, then it is
assumed to be unknown, not false.  Just because I've asserted that the
photo depicts Paris doesn't make it wrong, a priori, that it also depicts
Tokyo (it could be a montage).  It would also depict many other things
beyond Paris even if it didn't depict Tokyo.

The side effect of this is that when you want to make explicit claims about
resources that are only true in a particular context, you cannot make the
claim about the resource in general.  As bodies (and targets) of
Annotations are web resources, not properties of the Annotation, if we want
to make claims about that resource in the context of the annotation, we
need a new resource ... which is a Specific Resource.

We already have this in the model to enable Selectors, States, Styles and
Scope.  You cannot make an assertion that an image has a segment described
by a Selector, as many annotators might annotate different segments of the
same image.  In the open world, all of those selectors are possible and
true ... so when looking at the graph you cannot distinguish which selector
belongs to which annotation.

Thus the Specific Resource stands for the Body or Target in the specific
context of the Annotation.  We can safely make assertions about the
Specific Resource, as we just created it for that purpose, without
colliding with other annotations' assertions.

Given that bodies have the same required features as targets, we have
Specific Resources for bodies.  For example, we could otherwise not say
"this part of this web page is about that part of that image".  Or this
blog at this point in time is about that news article.  This part of this
video is about that part of that data set. And so forth.

Thus, and there will be a test on this next class, we cannot make
annotation specific assertions about either the body or the target directly
on the resource and motivation is (clearly) an annotation specific
assertion, not a global one. We already have a solution for that, which is
the specific resource construction.  This leads to the proposal to allow
motivatedBy on specific resources. (Or potentially and more radically, to
an alternative to do away with multiple bodies completely and have
annotation sets as first class objects)


Thanks and hope that helps!

Rob


-- 
Rob Sanderson
Information Standards Advocate
Digital Library Systems and Services
Stanford, CA 94305