Re: representing hypermedia controls in RDF

<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.



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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
>
>
>