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Subject: Feedback on draft-nottingham-http-link-header-04.txt


Eran, Mark, here is my feedback on:

http://www.ietf.org/internet-drafts/draft-nottingham-http-link-header-04.txt


A) I very much like the term "context IRI" in section 3 - I think that's a
great name for it. (On that score, it makes me think that the best name for
what's now /host-meta is actually /context-meta, but I'll save that for
feedback on that spec.)


B) This is purely an editorial suggestion. You say:

   A link can be viewed as a statement of the form "(context IRI) has a
   (relation type) resource at (target IRI)."

Given that the context URI, relation type (string), and target URI
essentially form an RDF triple (the only difference being that the relation
type may not be an absolute URI), I was thinking:

   A link can be viewed as a statement of the form "(context IRI) has a
   relation of (relation type) to the resource at (target IRI)."


C) In section 4:

   As such, relation types are not format-specific, and MUST NOT specify
   a particular format or media type that they are to be used with.
   Likewise, the context IRI for a given link is usually determined by
   the serialisation of the link (e.g., the Link header, a HTML
   document, etc.); a relation type SHOULD NOT specify the context IRI.

This confuses me because I can't figure our how the relation type even
_could_ specify the context URI. It's like saying an RDF predicate should
not be the RDF subject. It's nonsensical to begin with -- unless I'm missing
something (which I probably am).


D) In section 5:

   Each link-value conveys one target IRI as a URI-Reference (after
   conversion, if necessary) inside angle brackets ("<>").  If the URI-
   Reference is relative, it MUST be resolved as per [RFC3986].  Note
   that any base IRI from the body's content is not applied.

This para is too dense for me to clearly understand (or maybe I'm just being
too dense). It says, "...after conversion, if necessary..." -- which I
assume means conversion of the IRI to a URI-Reference -- however it's
unclear when such conversion is necessary. Why not just spell it out (see
also my final comment below about IRI ==> URI transformation in general).

Secondly, plenty of technical folks I know don't understand the concept of
"resolving" a relative URI-Reference - that could use another sentence of
explanation.

The third sentence, "Note that any base IRI from the body's content is not
applied" also needs more explanation as I'm not even sure what its referring
to. (Again, maybe I'm dense.)


E) Second 5:

   Normally, the relation type of a link is conveyed in the "rel"
   parameter's value.  The "rev" parameter has also been used for this
   purpose historically by some formats, and is included here for
   compatibility with those uses, but its use is not encouraged nor
   defined by this specification.

I know this whole "rev" thing is a huge can of worms, but don't you think it
deserves a little more explanation as to why it is confusing? Or at least a
reference to the slightly longer explanation you provide in Appendix A?

And maybe this deserves a SHOULD NOT rather than just "...is not
encouraged..."?


F) Section 5:

   Note that link-values may convey multiple links between the same
   target and context IRIs; for example

       Link: <http://example.org/>; rel=index;
             rel="start http://example.net/relation/other";

   Here, the link to "http://example.org/"; has the registered relation
   types "index" and "start", and the extension relation type
   "http://example.net/relation/other";.

This particular example seems unnecessarily tricky if it is going to be the
only example, i.e., two rels with the second one having two values. 

I would strongly recommend inserting a new section between 5 and 6 that is
only examples. Include 5-6 examples, starting with several very simple and
straightforward (the 80% case) and then including a few more advanced
examples such as the above to illustrate the extreme cases.


G) Appendix A:

   In HTML4, the link element can be mapped to links as specified here
   by using the "href" attribute for the target URI, and "rel" to convey
   both the relation type, as in the Link header.  The context of the
   link is the URI associated with the entire HTML document.

The word "both" before "the relation type" does not make sense - something
appears to be missing.


H) Overall I have found that the importance of the relationship and
transformation rules between IRIs and URIs are not well understood even by
many of whom you would expect it. So I would recommend this aspect of the
spec be beefed up, i.e., perhaps even given its own subsection.


Hope this helps,

=Drummond 




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