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Re: claimed completion of ACTION-97 - proposal for pure-HTTP paging

From: Eric Prud'hommeaux <eric@w3.org>
Date: Mon, 23 Sep 2013 18:27:14 -0400
To: Steve Speicher <sspeiche@gmail.com>
Cc: "public-ldp-wg@w3.org" <public-ldp-wg@w3.org>
Message-ID: <20130923222713.GD29518@w3.org>
* Steve Speicher <sspeiche@gmail.com> [2013-09-23 14:53-0400]
> Hey Eric,
> 
> +1 but a question below...
> 
> On Sat, Sep 21, 2013 at 9:40 PM, Eric Prud'hommeaux <eric@w3.org> wrote:
> 
> > Find the <PROPOSAL/> 44 lines down.
> >
> > TimBL's comment LC-2836 proposed moving page control out of the body
> > of an LDPR and into headers.
> > <https://www.w3.org/2006/02/lc-comments-tracker/55082/ldp/2836?cid=2836>
> >
> > This buys us:
> >   • Potential reuse outside of LDPRs.
> >   • Unrestricted data in an LDPR (screw case: an LDPR which includes a
> >     page from another LDPR).
> >
> > The first example in the LDP LC decribes how a GET on <resourceURL>
> > 303's (now 208½'s?) to e.g. <resourceURL>?firstPage, or OPTIONS on
> > <resourceURL> yields:
> >   Link: <resourceURL>?firstPage; rel="first"
> > The content of <resourceURL>?firstPage includes client data plus this
> > paging data:
> >
> > [[
> > <http://example.org/customer-relations?firstPage>
> >    a ldp:Page;
> >    ldp:pageOf <http://example.org/customer-relations>;
> >    ldp:nextPage <http://example.org/customer-relations?p=2>.
> > ]] <http://www.w3.org/TR/ldp/#ldpr-PagingIntro> (can we have an anchor
> >    on the <div class="example"/> elements?)
> >
> > The paging in this example is a singly-linked list split across HTTP
> > and the payload. We can move it all into HTTP (for the reasons above)
> > using link types defined in RFC5988 Web Linking:
> >
> > first      - An IRI that refers to the furthest preceding resource in a
> >              series of resources.
> > last       - An IRI that refers to the furthest following resource in a
> >              series of resources.
> > previous   - Refers to the previous resource in an ordered series of
> >              resources
> > next       - Refers to the next resource in a ordered series of resources.
> >
> > The type arc can come from RFC6903 Additional Link Relation Types:
> > type      - Refers to a resource identifying the abstract semantic
> >             type of which the link's context is considered to be an
> >             instance.
> >
> >
> > <PROPOSAL>
> > • GETs and OPTIONS on <resourceURL> remain the same.
> >
> > • GET/HEAD on <resourceURL>?firstPage returns purely user content with:
> >     Link: http://www.w3.org/ns/ldp#Page; rel=type
> >     Link: <resourceURL>?page2; rel=next
> >
> > • Lack of a Link: rel=next means you're at the end (closed HTTP world).
> >
> > • GET/OPTIONS on "doubly-linked servers" return an addtional last linl:
> >   Link: <resourceURL>?page2; rel="last"
> >
> 
> Why does this imply "doubly-linked servers" and why do you call this out
> and not "first"?

My proposal is intended to cover two cases, the original expressivity
of the navigation data that was in the RDF payload (which I would
describe as being navigated like a singly-linked list) and a more
expressive "doubly-linked" mode which delivers both the head and tail:
  Link: <resourceURL>?firstPage; rel="first"
  Link: <resourceURL>?page2; rel="last"

I expect that many applications will benefit from being able to skip
to the end, and RFC5988 already provided the vocabulary, so it seemed
like a pretty natural feature. I'm not a big fan of optional features,
but since back-traversal wasn't in the original langauge, I didn't
feel entitled to add it when migrating to HTTP headers. Also the
singly-linked server could be implemented with static content, unaware
of what had been appended to the end of the list, and I didn't want to
take away that feature. Zat make sense?


>  - Steve Speicher
> 
> 
> > • GET/HEAD on <resourceURL>?page2 on "doubly-linked servers" includes
> >     Link: <resourceURL>?firstPage; rel=previous
> > </PROPOSAL>
> >
> >
> > I prefer these link types to others in the IANA registry:
> > <http://www.iana.org/assignments/link-relations/link-relations.xhtml>
> >
> > RFC6903 Additional Link Relation Types:
> > about      - Refers to a resource that is the subject of the link's
> > context.
> >
> > RFC6573 The Item and Collection Link Relations:
> > collection - The target IRI points to a resource which represents the
> >              collection resource for the context IRI.
> > item       - The target IRI points to a resource that is a member of
> >              the collection represented by the context IRI.
> >
> > POWDER:
> > describedBy
> > RFC6892 The 'describes' Link Relation Type:
> > describes
> >
> > RFC6906 The 'profile' Link Relation Type:
> > profile    - Identifying that a resource representation conforms to
> >              a certain profile, without affecting the non-profile
> >              semantics of the resource representation.
> > --
> > -ericP
> >
> >

-- 
-ericP
Received on Monday, 23 September 2013 22:27:44 UTC

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