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Re: [rest-discuss] Re: Understanding Steady States

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  • Jan Algermissen
    ... Yep. http://www.imc.org/atom-protocol/mail-archive/msg11487.html ... The requirement that a GET on a collection returns an Atom feed. That is unRESTful
    Message 1 of 27 , Feb 1, 2010
      On Feb 2, 2010, at 4:16 AM, wahbedahbe wrote:

      >
      > --- In rest-discuss@yahoogroups.com, Jan Algermissen <algermissen1971@...> wrote:
      >> On Feb 1, 2010, at 2:54 PM, Mike Kelly wrote:
      >>> Jan Algermissen wrote:
      >>>> On Feb 1, 2010, at 1:38 PM, Mike Kelly wrote:
      >>>>> I think we need to agree on the definition of 'meaning' in this
      >>>>> context.. because, to me, it includes more than just the current set of
      >>>>> available link relations, and since we're not supposed to type resources
      >>>>> - the only approach I can see working is predefined application flows
      >>>>>
      >>>>
      >>>> Predefined application flows violate the hypermedia constraint and couple the server in a way that REST deliberately aims to avoid.
      >>>>
      >>>
      >>> Predefined application flows like AtomPub violate the hypermedia constraint?
      >>
      >> Yes. Roy confirmed that (recent post on atom-protocol list)
      >
      >
      > Really? Can you link to that? Was it the "MUST a collection be returned as an Atom feed?" thread?

      Yep. http://www.imc.org/atom-protocol/mail-archive/msg11487.html

      >
      > I didn't read any of Roy's comments that way... or maybe I don't understand what you mean by "AtomPub's predefined flow".

      The requirement that a GET on a collection returns an Atom feed. That is unRESTful coupling because the client must not rely on such information but react to whatever it gets at runtime.

      >
      > Do you mean the Service -> Feed -> Entry hierarchy?

      Yes, that's what it comes down to.

      >
      > You said yourself in that thread that <collection> and <image> played conceptually similar roles. Isn't Page -> Image a similar two-level hierarchy? What is wrong with that?

      <collection href=""> points to 'a collection', that is ok. But predefining the media type that comes back from the collection is not. Might well be RSS or text/uri-list


      >
      > I guess what I'm wondering is if AtomPub really defines an
      > "application flow" or do client writers mistake the hierarchy for one?

      A truly RESTful client would do a GET on the collection and treat any response as 'correct' from a server POV (except for non-Collection representations, for
      example an audio file).

      Only if we do that the server's independent evolvability is preserved.

      Jan

      >
      > Regards,
      >
      > Andrew
      >
      >
      >
      > ------------------------------------
      >
      > Yahoo! Groups Links
      >
      >
      >

      -----------------------------------
      Jan Algermissen, Consultant

      Mail: algermissen@...
      Blog: http://www.nordsc.com/blog/
      Work: http://www.nordsc.com/
      -----------------------------------
    • Mike Kelly
      ... That post is about over-specification, not predefinition. And leads me to ask - What is an adequate specification , if not predefinition? - Mike
      Message 2 of 27 , Feb 2, 2010
        Jan Algermissen wrote:
        > On Feb 2, 2010, at 4:16 AM, wahbedahbe wrote:
        >
        >
        >> --- In rest-discuss@yahoogroups.com, Jan Algermissen <algermissen1971@...> wrote:
        >>
        >>> On Feb 1, 2010, at 2:54 PM, Mike Kelly wrote:
        >>>
        >>>> Jan Algermissen wrote:
        >>>>
        >>>>> On Feb 1, 2010, at 1:38 PM, Mike Kelly wrote:
        >>>>>
        >>>>>> I think we need to agree on the definition of 'meaning' in this
        >>>>>> context.. because, to me, it includes more than just the current set of
        >>>>>> available link relations, and since we're not supposed to type resources
        >>>>>> - the only approach I can see working is predefined application flows
        >>>>>>
        >>>>>>
        >>>>> Predefined application flows violate the hypermedia constraint and couple the server in a way that REST deliberately aims to avoid.
        >>>>>
        >>>>>
        >>>> Predefined application flows like AtomPub violate the hypermedia constraint?
        >>>>
        >>> Yes. Roy confirmed that (recent post on atom-protocol list)
        >>>
        >> Really? Can you link to that? Was it the "MUST a collection be returned as an Atom feed?" thread?
        >>
        >
        > Yep. http://www.imc.org/atom-protocol/mail-archive/msg11487.html
        >

        That post is about over-specification, not predefinition. And leads me
        to ask - What is an 'adequate specification', if not predefinition?

        - Mike
      • Jan Algermissen
        ... I understood Roy to be saying that it is an over-specifiction that AtomPub requires GETs on collections to return an Atom feed. Such a predefinition is an
        Message 3 of 27 , Feb 2, 2010
          On Feb 2, 2010, at 11:25 AM, Mike Kelly wrote:

          > Jan Algermissen wrote:
          >> On Feb 2, 2010, at 4:16 AM, wahbedahbe wrote:
          >>
          >>
          >>> --- In rest-discuss@yahoogroups.com, Jan Algermissen <algermissen1971@...> wrote:
          >>>
          >>>> On Feb 1, 2010, at 2:54 PM, Mike Kelly wrote:
          >>>>
          >>>>> Jan Algermissen wrote:
          >>>>>
          >>>>>> On Feb 1, 2010, at 1:38 PM, Mike Kelly wrote:
          >>>>>>
          >>>>>>> I think we need to agree on the definition of 'meaning' in this
          >>>>>>> context.. because, to me, it includes more than just the current set of
          >>>>>>> available link relations, and since we're not supposed to type resources
          >>>>>>> - the only approach I can see working is predefined application flows
          >>>>>>>
          >>>>>>>
          >>>>>> Predefined application flows violate the hypermedia constraint and couple the server in a way that REST deliberately aims to avoid.
          >>>>>>
          >>>>>>
          >>>>> Predefined application flows like AtomPub violate the hypermedia constraint?
          >>>>>
          >>>> Yes. Roy confirmed that (recent post on atom-protocol list)
          >>>>
          >>> Really? Can you link to that? Was it the "MUST a collection be returned as an Atom feed?" thread?
          >>>
          >>
          >> Yep. http://www.imc.org/atom-protocol/mail-archive/msg11487.html
          >>
          >
          > That post is about over-specification, not predefinition. And leads me
          > to ask - What is an 'adequate specification', if not predefinition?

          I understood Roy to be saying that it is an over-specifiction that AtomPub requires GETs on collections to return an Atom feed.

          Such a predefinition is an over-specification in RESTland.

          Jan

          >
          > - Mike
          >
          >
          > ------------------------------------
          >
          > Yahoo! Groups Links
          >
          >
          >

          -----------------------------------
          Jan Algermissen, Consultant
          NORD Software Consulting

          Mail: algermissen@...
          Blog: http://www.nordsc.com/blog/
          Work: http://www.nordsc.com/
          -----------------------------------
        • Mike Kelly
          ... Maybe so, but the use of term over specification implies that there is infact an appropriate degree of specification i.e. a predefined flow with a more
          Message 4 of 27 , Feb 2, 2010
            Jan Algermissen wrote:
            > On Feb 2, 2010, at 11:25 AM, Mike Kelly wrote:
            >
            >
            >> Jan Algermissen wrote:
            >>
            >>> On Feb 2, 2010, at 4:16 AM, wahbedahbe wrote:
            >>>
            >>>
            >>>
            >>>> --- In rest-discuss@yahoogroups.com, Jan Algermissen <algermissen1971@...> wrote:
            >>>>
            >>>>
            >>>>> On Feb 1, 2010, at 2:54 PM, Mike Kelly wrote:
            >>>>>
            >>>>>
            >>>>>> Jan Algermissen wrote:
            >>>>>>
            >>>>>>
            >>>>>>> On Feb 1, 2010, at 1:38 PM, Mike Kelly wrote:
            >>>>>>>
            >>>>>>>
            >>>>>>>> I think we need to agree on the definition of 'meaning' in this
            >>>>>>>> context.. because, to me, it includes more than just the current set of
            >>>>>>>> available link relations, and since we're not supposed to type resources
            >>>>>>>> - the only approach I can see working is predefined application flows
            >>>>>>>>
            >>>>>>>>
            >>>>>>>>
            >>>>>>> Predefined application flows violate the hypermedia constraint and couple the server in a way that REST deliberately aims to avoid.
            >>>>>>>
            >>>>>>>
            >>>>>>>
            >>>>>> Predefined application flows like AtomPub violate the hypermedia constraint?
            >>>>>>
            >>>>>>
            >>>>> Yes. Roy confirmed that (recent post on atom-protocol list)
            >>>>>
            >>>>>
            >>>> Really? Can you link to that? Was it the "MUST a collection be returned as an Atom feed?" thread?
            >>>>
            >>>>
            >>> Yep. http://www.imc.org/atom-protocol/mail-archive/msg11487.html
            >>>
            >>>
            >> That post is about over-specification, not predefinition. And leads me
            >> to ask - What is an 'adequate specification', if not predefinition?
            >>
            >
            > I understood Roy to be saying that it is an over-specifiction that AtomPub requires GETs on collections to return an Atom feed.
            >
            > Such a predefinition is an over-specification in RESTland.
            >
            > Jan
            >

            Maybe so, but the use of term "over" specification implies that there is
            infact an appropriate degree of specification i.e. a predefined flow
            with a more suitable level of liberalism.

            - Mike
          • wahbedahbe
            ... Ok... agree on the above, but how do you define collection ? To me it s something that has a set of entries . So you get the hierarchy don t you? A
            Message 5 of 27 , Feb 2, 2010
              --- In rest-discuss@yahoogroups.com, Jan Algermissen <algermissen1971@...> wrote:
              >
              >
              > On Feb 2, 2010, at 4:16 AM, wahbedahbe wrote:
              >
              > >
              > > --- In rest-discuss@yahoogroups.com, Jan Algermissen <algermissen1971@> wrote:
              > >> On Feb 1, 2010, at 2:54 PM, Mike Kelly wrote:
              > >>> Jan Algermissen wrote:
              > >>>> On Feb 1, 2010, at 1:38 PM, Mike Kelly wrote:
              > >>>>> I think we need to agree on the definition of 'meaning' in this
              > >>>>> context.. because, to me, it includes more than just the current set of
              > >>>>> available link relations, and since we're not supposed to type resources
              > >>>>> - the only approach I can see working is predefined application flows
              > >>>>>
              > >>>>
              > >>>> Predefined application flows violate the hypermedia constraint and couple the server in a way that REST deliberately aims to avoid.
              > >>>>
              > >>>
              > >>> Predefined application flows like AtomPub violate the hypermedia constraint?
              > >>
              > >> Yes. Roy confirmed that (recent post on atom-protocol list)
              > >
              > >
              > > Really? Can you link to that? Was it the "MUST a collection be returned as an Atom feed?" thread?
              >
              > Yep. http://www.imc.org/atom-protocol/mail-archive/msg11487.html
              >
              > >
              > > I didn't read any of Roy's comments that way... or maybe I don't understand what you mean by "AtomPub's predefined flow".
              >
              > The requirement that a GET on a collection returns an Atom feed. That is unRESTful coupling because the client must not rely on such information but react to whatever it gets at runtime.
              >
              > >
              > > Do you mean the Service -> Feed -> Entry hierarchy?
              >
              > Yes, that's what it comes down to.
              >
              > >
              > > You said yourself in that thread that <collection> and <image> played conceptually similar roles. Isn't Page -> Image a similar two-level hierarchy? What is wrong with that?
              >
              > <collection href=""> points to 'a collection', that is ok. But predefining the media type that comes back from the collection is not. Might well be RSS or text/uri-list
              >
              >
              > >
              > > I guess what I'm wondering is if AtomPub really defines an
              > > "application flow" or do client writers mistake the hierarchy for one?
              >
              > A truly RESTful client would do a GET on the collection and treat any response as 'correct' from a server POV (except for non-Collection representations, for
              > example an audio file).
              >
              > Only if we do that the server's independent evolvability is preserved.
              >

              Ok... agree on the above, but how do you define 'collection'? To me it's something that has a set of 'entries'. So you get the hierarchy don't you? A 'good' client can/should be flexible on the media types though (and the spec shouldn't try to restrict them). Perhaps the variability in media type means that the entries may be exclusively inline for some representations which just means that the hierarchy might not map to your addressable resources, but it's still there.


              Andrew
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