Re: New Version Notification for draft-divilly-atom-hierarchy-01

[Al Brown <[e-mail]>]

Nikunj wrote:
>     Al Brown wrote:


      b. add a new attribute to link that specifies if they are inlined
      (down) <link rel="down" href="http://www.example.com/foo/down" />
      (down-tree) <link rel="down" ah:inlined="true" href="
      http://www.example.com/foo/down/inlined" />
      This adds complexity if there are cardinality constraints on link
      relations such as alternate and clients not aware of I-D may think
      they are the same.


>IMHO, ah:inlined does nothing because the presence of ae:inline makes it
plenty clear. If you were trying to say that there is a certain level of
depth in the tree, may >be an attribute would help, but even then you don't
know what things the server may have elided from every entry. So, bottom
line is, there is not much value to an >attribute to describe the thing
that is in-lined. You are best off using what you have received as an
approximation and then get the exact representation if you care so >much in
a separate network call. Of course, out-of-band communication or
specialized mark-up may provide enough information for you to avoid such
round-trips.


Maybe I did not explain clearly enough - this is a protocol/hypermedia
issue.  How does the client say (follow the right link relation) I want an
inlined representation of this resource specified by a link relation?
E.g.,


Client (C) navigates to this atom entry (A) somehow.  A wants to advertise
to the client that A has references to two to representations for resource
B.  One version of B is flat (ala a feed).  One version of B is the same
flat feed with its link relations inlined (ala tree).


How can resource A provide the client C with information there are two
choices available for B (flat vs tree)?


-Al



Al Brown
Emerging Standards and Industry Frameworks
CMIS: https://w3.tap.ibm.com/w3ki07/display/ECMCMIS/Home
Industry Frameworks: https://w3.tap.ibm.com/w3ki07/display/ECMIF/Home

Office 714 327 3453
Mobile [phone]
Email  [e-mail]
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  From:       "Nikunj R. Mehta" <[e-mail]>                                                                       
                                                                                                                                
  To:         Al Brown/Costa Mesa/IBM@IBMUS                                                                                     
                                                                                                                                
  Cc:         James M Snell <[e-mail]>, atom-syntax Syntax <[e-mail]>                                       
                                                                                                                                
  Date:       06/08/2009 03:33 PM                                                                                               
                                                                                                                                
  Subject:    Re: New Version Notification for draft-divilly-atom-hierarchy-01                                                  
                                                                                                                                





As I see it, whether there is a @rel=down-tree or not, you would have to
communicate certain information out-of-band, e.g., depth of the tree or the
level of completeness in every in-lined entry.

Atom does not provide any means of advertising URIs for retrieving
representation variants. This could be a source of your dissatisfaction but
it applies equally well regardless of hierarchy or in-lining.

On Jun 8, 2009, at 3:11 PM, Al Brown wrote:



      James wrote:
      >Hmmm.... I know we've discussed this, but after thinking about it
      more
      >and looking through the examples, I'm becoming increasingly less
      >convinced that we need a distinction between "down" and "down-tree".

      >One should simply assume that "down" could point to a child entry or

      >child feed and that those children could potentially also be
      parents.
      >Yes, that possibly increases the processing compexity but I think it

      >simplifies the model overall.

      We've discussed this today on the phone.  For me this is a difference
      of protocol/hypermedia vs. syntax.  For syntax, "down" and "up" are
      sufficient.  A flat model can modeled with feed and a tree can be
      modeled using generic inlining in a feed or entry.

      A client requests an atom document - entry or feed.  How does the
      server advertise to the client, via what is in the atom document,
      here are two links to representations (flat vs. tree) of a resource,
      e.g. the folder's children:  one link returns a flat list (no
      inlining) and one link returns a tree (inlined).


It is no different from seeing an HTML vs. a PDF representation of the same
blog entry. One gives you a lot of context such as comments, related posts,
advertisements and the like, and the other may be limited. This problem,
AFAICT, exists regardless of CMIS or hierarchy.


      Both are the same document just with or without inlining of linked
      resources of a particular link relation.


For all practical purposes, they are different documents, i.e., different
representations of a single resource.



      Since the resources are crossing the wire, the first resource (e.g.,
      folder) needs to convey how access a hierarchical resource (e.g.,
      items in a folder) in either a flat mode (feed) or tree (feed with
      inlined resources).

      The options I see are:
      a. append -tree to link relations that may inline (e.g., down-tree,
      up-tree). Not so nice, but works.


It may not be specific enough anyway to say this is a tree link because it
says nothing about depth


      b. add a new attribute to link that specifies if they are inlined
      (down) <link rel="down" href="http://www.example.com/foo/down" />
      (down-tree) <link rel="down" ah:inlined="true" href="
      http://www.example.com/foo/down/inlined" />
      This adds complexity if there are cardinality constraints on link
      relations such as alternate and clients not aware of I-D may think
      they are the same.


IMHO, ah:inlined does nothing because the presence of ae:inline makes it
plenty clear. If you were trying to say that there is a certain level of
depth in the tree, may be an attribute would help, but even then you don't
know what things the server may have elided from every entry. So, bottom
line is, there is not much value to an attribute to describe the thing that
is in-lined. You are best off using what you have received as an
approximation and then get the exact representation if you care so much in
a separate network call. Of course, out-of-band communication or
specialized mark-up may provide enough information for you to avoid such
round-trips.


      c. leverage link templates rather than link relations


I am not aware of "link templates". If you are referring to
draft-gregorio-uri-templates, then too there is no notion of templates
baked in to the link element yet.


      d. use out of band communication - append a uri argument such as
      includeLinkRel=down to the URI of the resource; could also be HTTP
      header. Not very RESTful but works.

      If the model is not sufficient to convey to the client here's a flat
      mode vs. here's a tree mode, CMIS will have to find another
      alternative as it is currently required by the CMIS domain model.

      I see the options for CMIS as:
      1. Leverage the model specified by the I-D if exists (best)
      2. Move down-tree to CMIS namespace. This does not solve the
      protocol/hypermedia problem for anybody else.
      3. Specify in the CMIS specification an URI argument to enable
      inlining of 'down'.

      -Al

      Al Brown
      Emerging Standards and Industry Frameworks
      CMIS: https://w3.tap.ibm.com/w3ki07/display/ECMCMIS/Home
      Industry Frameworks: https://w3.tap.ibm.com/w3ki07/display/ECMIF/Home

      Office 714 327 3453
      Mobile [phone]
      Email [e-mail]
      CONFIDENTIAL NOTICE: The contents of this message, including any
      attachments, are confidential and are intended solely for the use of
      the person or entity to whom the message was addressed. If you are
      not the intended recipient of this message, please be advised that
      any dissemination, distribution, or use of the contents of this
      message is strictly prohibited. If you received this message in
      error, please notify the sender. Please also permanently delete all
      copies of the original message and any attached documentation.

      <graycol.gif>James M Snell ---06/08/2009 11:55:37 AM---Comments
      below...
                                                                           
 <ecblan <ecblank.gif>                                                     
 k.gif>  James M Snell <[e-mail]>                                 
 From:                                                                     
                                                                           
 <ecblan <ecblank.gif>                                                     
 k.gif>  Al Brown/Costa Mesa/IBM@IBMUS                                     
 To:                                                                       
                                                                           
 <ecblan <ecblank.gif>                                                     
 k.gif>  "Nikunj R. Mehta" <[e-mail]>, Atom-Syntax Syntax < 
 Cc:     [e-mail]>, [e-mail]              
                                                                           
 <ecblan <ecblank.gif>                                                     
 k.gif>  06/08/2009 11:55 AM                                               
 Date:                                                                     
                                                                           
 <ecblan <ecblank.gif>                                                     
 k.gif>  Re: Fwd: New Version Notification for                             
 Subject draft-divilly-atom-hierarchy-01                                   
 :                                                                         
                                                                           







      Comments below...

      Al Brown wrote:
      >
      > The 01 draft is a much better. I am concerned the generic mechanism

      > using inlining links is sub-optimal for displaying a hierarchy that

      > this I-D helps navigate via the new link relations.
      >
      in-lining arbitrarily complex hierarchies is always going to be
      problematic and suboptimal... which is why I was so adamant about not

      baking hierarchy into Atom and Atompub in the first place when we
      were
      working on all this stuff initially.  Despite the added verbosity
      that
      this approach adds, however, I think it's likely the most acceptable
      approach.

      > First example: there are two down relations: down and down-tree. It
      is
      > important to have both of those link relations on the [standalone]
      > atom entry that represents a folder so the client can chose a flat
      > (feed) or tree (expanded feed) representation. If the client
      chooses
      > the tree representation, then on the atom feed returned the server
      > will inline using the link relation down. down-tree is not expanded

      > with content inline. E.g.,
      >
      > <atom:entry>
      > ...
      > <!-- children level 1 -->
      > <atom:link rel="down" type="application/atom+xml;type=feed"
      > href="/finance/feeds/default/portfolios/1/positions">
      > <ae:inline>
      > <atom:feed>
      > <!-- /a -->
      > <atom:entry>
      > ...
      > <!-- children level 2 for /a -->
      > <atom:link rel="down"
      > href="/finance/feeds/default/portfolios/1/positions"/>
      > ...
      > <ae:inline>
      > <atom:feed>
      > <!-- entry /a/1 -->
      > <atom:entry>
      > ...
      > <atom:link rel="down"
      > href="/finance/feeds/default/portfolios/1/positions/down">
      > <!-- repeats -->
      > </atom:link>
      > <atom:link rel="down-tree"
      > href="/finance/feeds-tree/default/portfolios/1/positions/down" />
      >
      > ...
      > </atom:entry>
      > </atom:feed>
      > </ae:inline>
      > <atom:entry>...</atom:entry>
      > <atom:entry>...</atom:entry>
      > </atom:feed>
      > </ae:inline>
      > </atom:link>
      > <atom:link rel="down-tree" type="application/atom+xml;type=feed"
      > href="/finance/feeds-tree/default/portfolios/1/positions" />
      >
      > ...
      > </atom:entry>
      >
      > The contents of the down link relation will be what should be
      included
      > in the down-tree due to recursion through the atom entries. Having
      a
      > separate extension element, side-steps this issue of expression.
      >
      Hmmm.... I know we've discussed this, but after thinking about it
      more
      and looking through the examples, I'm becoming increasingly less
      convinced that we need a distinction between "down" and "down-tree".

      One should simply assume that "down" could point to a child entry or
      child feed and that those children could potentially also be parents.

      Yes, that possibly increases the processing compexity but I think it
      simplifies the model overall.

      > Second example: verbosity
      > This proposal now has:
      > <atom:entry>
      > ...
      > <atom:link rel="down" type="application/atom+xml;type=feed"
      > href="/finance/feeds/default/portfolios/1/positions">
      > <ae:inline>
      > <atom:feed>
      > <atom:link rel="self"
      > href="/finance/feeds/default/portfolios/1/positions"/>
      > ...
      > <atom:entry>...</atom:entry>
      > <atom:entry>...</atom:entry>
      > <atom:entry>...</atom:entry>
      > </atom:feed>
      > </ae:inline>
      > </atom:link>
      > ...
      > </atom:entry>
      >
      > instead of a simpler mechanism:
      > <atom:entry>
      > ...
      > <ah:include rel="down">
      > <atom:entry>...</atom:entry>
      > <atom:entry>...</atom:entry>
      > <atom:entry>...</atom:entry>
      > </ah:include>
      > ...
      > </atom:entry>
      >
      > The I-D introduces a concept of hierarchy through
      > up/up-tree/down-tree/down relations yet a all-purpose mechanism for

      > inclusion. Most (all?) of the information on the feed element is
      > duplicated on the enclosing entry (id, uri, etc). Can't we do
      better
      > for this specific scenario the I-D is addressing?
      >
      I think we can address this by eliminating the restriction that
      "down"
      and "up" must always point to Atom feed documents and by changing the

      cardinality rules for those links. That restriction, I think, is
      arbitrary and unnecessary

      It would allow us to do something like....

      <atom:entry>
      ...
      <atom:link rel="down" type="application/atom+xml;type=entry"
      href="child1">
      <ae:inline>
      <atom:entry>...</atom:entry>
      </ae:inline>
      </atom:link>
      <atom:link rel="down" type="application/atom+xml;type=entry"
      href="child2">
      <ae:inline>
      <atom:entry>...</atom:entry>
      </ae:inline>
      </atom:link>
      ...
      <atom:link rel="down" type="application/atom+xml;type=entry"
      href="childN">
      <ae:inline>
      <atom:entry>...</atom:entry>
      </ae:inline>
      </atom:link>
      ...
      </atom:entry>

      Unlike any of the other methods discussed, this approach would allow
      clients that don't understand the hierarchy model to still understand

      that there is some kind of link relationship with each of the
      individual
      child resources and eliminates the need to include the extraneous
      atom:feed metadata.

      Note that this is the same basic approach taken by my comment thread
      extension (in-reply-to).

      - James