Re: representing hypermedia controls in RDF

see, even more affordances. ;)



mamund
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On Tue, Nov 26, 2013 at 9:59 AM, Kingsley Idehen <kidehen@openlinksw.com>wrote:

>  On 11/26/13 9:48 AM, mike amundsen wrote:
>
> Martynas:
>
>  No "by extension" needed here. Affordance is a quality of a thing that
> allows action.
>
>  RDF alone (w/o an added ontology) affords "data interchange."
>
>
> RDF on its own does offer a little more than data interchange. It enables
> structured data representation where actual relationship semantics are
> discernible and comprehensible by both humans and machines.
>
>
> Kingsley
>
>
>
> On Tue, Nov 26, 2013 at 7:24 AM, Martynas Jusevičius <
> martynas@graphity.org> wrote:
>
>> Mike,
>>
>> You wrote
>>
>> > Yes,
>> >
>> > <http://example.com/xxxxx> a foaf:Image .
>> >
>> > is an affordance.
>>
>>  Then, by extension, RDF classes are affordances, and vocabularies are
>> specifications of them.
>> So this gives me the impression that Linked Data applications can
>> solve the affordance issue using the standard components that have
>> always been there - RDF and vocabularies/ontologies?
>>
>> Martynas
>> graphityhq.com
>>
>>
>> >
>> > of course, that affordance (like HTML.IMG) relies a number of
>> expectations
>> > which most all of us recognize when we see it.
>> >
>> > From the network perspective, the expectations are (to keep it simple):
>> > - this is a "safe"[1] and "idempotent"[2] operation
>> > - an image media type to be returned.
>> >
>> > From the client application perspective, the expectations are:
>> > - use an HTTP.GET when executing this operation
>> > - take the results of the locator and "transclude" it into the existing
>> view
>> >
>> > if any these expectations are not fulfilled, the affordance is usually
>> > considered "broken" (the network failed) or "mis-used" (the client did
>> > something else).
>> >
>> > <snip>
>> > By the way, nothing stops me from having <a href="isbn:343-224122">
>> either.
>> > It will probably be clickable, but won't work.
>> > </snip>
>> > I would restate this as "it is *possible* to have..." since there is,
>> > actually something that stops you - the expectations of so many others
>> who
>> > recognize this affordance.
>> >
>> > Think of the HTML.A as a door in a room. If i go up to a door, turn the
>> > handle, and nothing happens (I don't "navigate" to a new room), I
>> consider
>> > the door broken or (as Donald Norman might say) that the door is "lying
>> to
>> > me." If I encounter a home where many of the doors act in this
>> unexpected
>> > way, I find the experience off-putting. I might even judge the architect
>> > incompetent to, at the least, perverse.
>> >
>> > Now consider a hypermedia representation where many of the affordances
>> are
>> > either not working as expected (as in your case) or are actually
>> inscrutable
>> > to me; ones that just don't tell me enough to be usable.
>> >
>> > There is an advantage to using affordances in that they offer a shared
>> > understanding without the need for narrative or instructions. That's
>> why we
>> > can drive most vehicles if we've already learned to drive one. Why we
>> can
>> > operate most telephones, etc.  Devices that have unfamiliar or
>> > counter-intuitive affordances are frustrating and, in some rare cases,
>> can
>> > be dangerous.
>> >
>> >
>> >
>> > [1] http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.1.1
>> > [2] http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html#sec9.1.2
>> >
>> >
>> > mamund
>> > +1.859.757.1449
>> > skype: mca.amundsen
>> > http://amundsen.com/blog/
>> > http://twitter.com/mamund
>> > https://github.com/mamund
>> > http://www.linkedin.com/in/mamund
>> >
>> >
>> > On Fri, Nov 22, 2013 at 12:16 PM, Martynas Jusevičius
>> > <martynas@graphity.org> wrote:
>> >>
>> >> Mike,
>> >>
>> >> so if RDF representation includes a triple such as
>> >>
>> >>   <http://example.com/xxxxx> a foaf:Image .
>> >>
>> >> is that an affordance? Because that gives me enough information to
>> >> render it as <img src="http://example.com/xxxxx"/>.
>> >>
>> >> By the way, nothing stops me from having <a href="isbn:343-224122">
>> >> either. It will probably be clickable, but won't work.
>> >>
>> >> Martynas
>> >>
>> >> On Fri, Nov 22, 2013 at 4:42 PM, mike amundsen <mamund@yahoo.com>
>> wrote:
>> >> > <snip>
>> >> > A browser for example doesn't render the string
>> >> > http://example.com/343-224122 as a clickable link unless you mark
>> it up
>> >> > as
>> >> > one using the <a> tag.
>> >> > </snip>
>> >> >
>> >> > Yep, the A element is the thing that _affords_ clicking. it is the A
>> >> > element
>> >> > which is the affordance.
>> >> >
>> >> > Affordances don't just supply addresses, they supply information
>> about
>> >> > what
>> >> > you can _do_ with that address (navigate, transclude, send arguments,
>> >> > write
>> >> > data, remove data, etc.). The appearance of a URL alone provides very
>> >> > little
>> >> > affordance.
>> >> >
>> >> > For example:
>> >> > - http://example.com/xxxxx
>> >> > - http://example.com/yyyyy
>> >> > one of the two URLs points to a blog page to which the user can
>> >> > navigate,
>> >> > the other points to a logo which should be displayed inline. which is
>> >> > which?
>> >> >
>> >> > Now this:
>> >> > - <a href="...">blog</a>
>> >> > - <img href="..."  />
>> >> > one of the two URLs points to a blog page, the other points to a
>> logo.
>> >> > which
>> >> > is which?
>> >> >
>> >> > Note it is not the URL that provides the information (which is for
>> >> > navigation, which is for transclusion), but the element in which the
>> URL
>> >> > appears. The element is the affordance. These are HTML affordances.
>> >> > There
>> >> > are a couple more hypermedia affordances in HTML. Other message
>> models
>> >> > (media types) contain their own affordances.
>> >> >
>> >> > It is the appearance of affordances within the response
>> representation
>> >> > that
>> >> > is a key characteristic of hypermedia messages.
>> >> >
>> >> >
>> >> >
>> >> > mamund
>> >> > +1.859.757.1449
>> >> > skype: mca.amundsen
>> >> > http://amundsen.com/blog/
>> >> > http://twitter.com/mamund
>> >> > https://github.com/mamund
>> >> > http://www.linkedin.com/in/mamund
>> >> >
>> >> >
>> >> > On Fri, Nov 22, 2013 at 10:13 AM, Markus Lanthaler
>> >> > <markus.lanthaler@gmx.net> wrote:
>> >> >>
>> >> >> Hi Martynas,
>> >> >>
>> >> >> On Friday, November 22, 2013 3:12 PM, Martynas Jusevičius wrote:
>> >> >> > Markus,
>> >> >> >
>> >> >> > in the Linked Data context, what is the difference between
>> >> >> > "identifier" and "hyperlink"? Last time I checked, URIs were
>> opaque
>> >> >> > and there was no such distinction.
>> >> >>
>> >> >> These things quickly turn into philosophical discussions but simply
>> >> >> speaking
>> >> >> the difference lies in the expectations of a client. In XML for
>> >> >> example,
>> >> >> namespaces are just identifiers. There's no expectation that you
>> can go
>> >> >> and
>> >> >> dereference that namespace identifier (even though in most cases
>> they
>> >> >> use
>> >> >> HTTP URIs). The same is true about RDF. All URIs are just
>> identifiers.
>> >> >> From
>> >> >> an RDF point of view, there's no difference between isbn:343-224122
>> and
>> >> >> http://example.com/343-224122. As you say, they are opaque.
>> >> >>
>> >> >> But if you build applications, it is important to distinguish
>> between
>> >> >> identifiers and hyperlinks. A browser for example doesn't render the
>> >> >> string
>> >> >> http://example.com/343-224122 as a clickable link unless you mark
>> it up
>> >> >> as
>> >> >> one using the <a> tag.
>> >> >>
>> >> >> Linked Data advocates that all URIs are dereferenceable. But that's
>> >> >> communicated out of band. Apart from JSON-LD, which states that URIs
>> >> >> SHOULD
>> >> >> be dereferenceable, no other RDF media type makes such a statement.
>> >> >> Thus
>> >> >> you
>> >> >> need to use constructs such as hydra:Link and hydra:Resource to make
>> >> >> the
>> >> >> distinction explicit.
>> >> >>
>> >> >> Hope this helps. If not, let me know.
>> >> >>
>> >> >>
>> >> >> --
>> >> >> Markus Lanthaler
>> >> >> @markuslanthaler
>> >> >>
>> >> >>
>> >> >
>> >
>> >
>> >
>>
>
>
>
> --
>
> Regards,
>
> Kingsley Idehen 
> Founder & CEO
> OpenLink Software
> Company Web: http://www.openlinksw.com
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>
>
>
>