Hi Stuart,

On Tue, May 7, 2013 at 4:37 PM, stuart yeates <[log in to unmask]>wrote:

> On 08/05/13 02:28, Owen Stephens wrote:
>  1) A highlighted span of text.  There is an obvious target segment of a
>> resource (the object), but there is no body/comment (the subject).  As a
>> triple must have a subject, this could not be expressed.  A second
>> example of this would be a bookmark where the body is also implicit.
> I'm not quite sure what you mean by "could not be expressed" Such use
> cases are readily expressed using the XPointer family of schemes. The best
> introduction to them I'm aware of is at**
> php/XPointer <> Members of the
> family exists in a variety of states of implementation and standardisation.

An RDF triple must have all three parts: subject, predicate, and object
The complaint was that an Annotation somehow expresses just a single triple
where the body is the subject, the predicate is derived from the motivation
or class, and the object is the target.
This example was to demonstrate that there are annotation use cases that
cannot be modeled as an RDF triple, as the body is not mandatory, whereas
the subject is.

 2) An annotation that refers to multiple segments of a resource,
>> multiple resources or multiple segments of multiple resources.  In this
>> case there would be multiple objects, which is also not possible to be
>> expressed in RDF.
> The W3C XPointer scheme at**xpointer/<>can point to any set of things pointable to by a single XPath 1.0
> expression.

Correct, but not everything in the world is XML and amenable to
Xpointer/Xpath processing :)
For example, non rectangular areas of an image cannot be expressed using
any existing URI fragment syntax.