Re: representing hypermedia controls in RDF

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 <mailto: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 <http://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 <tel:%2B1.859.757.1449>
>     > 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 <mailto: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 <mailto: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 <tel:%2B1.859.757.1449>
>     >> > 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 <mailto: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
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Received on Tuesday, 26 November 2013 14:59:46 UTC