Re: recommended pattern for markup-valued 'breadcrumb' properties in RDFa

Hi Dan,

Like Gregg, I'm not a big fan of shoving the whole breadcrumb items into a
single rdf:HTML value.

First maybe we should define what info you want to capture in the
breadcrumbs. I'm going to assume that you want to have the URL and the name
of each item, and each item should be typed with
http://schema.org/Breadcrumb (correct me if I'm wrong with this
assumption). If you're only interested in URLs or names only, the markup
becomes much simpler.

## 1. @rel and no schema:url

The simpler and shorter option involves just adding a span element inside
each breadcrumb item and wrapping everything with @rel and @inlist
attributes:

<div vocab="http://schema.org/" typeof="WebPage">
    <div rel="breadcrumb" inlist="">
      <a typeof="Breadcrumb" href="category/books.html"><span
property="name">Books</span></a> >
      <a typeof="Breadcrumb" href="category/books-literature.html"><span
property="name">Literature and Fiction</span></a> >
    </div>
</div>

which yields:

 [ a schema:WebPage;
    schema:breadcrumb (<category/books.html>
<category/books-literature.html>)] .

<category/books-literature.html> a schema:Breadcrumb;
   schema:name "Literature and Fiction" .

<category/books.html> a schema:Breadcrumb;
   schema:name "Books" .

I like this option the best because the markup is very succinct and doesn't
repeat any data. In this case, you don't get an explicit schema:url, but
instead you get this value from the URI of each breadcrumb resource (no
blank nodes either!).


## 2. no @rel and no schema:url

Like Gregg said, you can also assert @property for each item if you want to
avoid a wrapping @rel. This examples yields the same output as the previous
one:

<div vocab="http://schema.org/" typeof="WebPage">
    <div>
      <a property="breadcrumb" typeof="Breadcrumb" inlist=""
href="category/books.html"><span property="name">Books</span></a> >
      <a property="breadcrumb" typeof="Breadcrumb" inlist=""
href="category/books-literature.html"><span property="name">Literature and
Fiction</span></a> >
    </div>
</div>


## 3. @rel and schema:url

If an explicit schema:url is required, it is still possible at the expense
of more markup:

<div vocab="http://schema.org/" typeof="WebPage">
    <div rel="breadcrumb" inlist="">
      <span typeof="Breadcrumb"><a property="url"
href="category/books.html"><span property="name">Books</span></a></span> >
      <span typeof="Breadcrumb"><a property="url"
href="category/books-literature.html"><span property="name">Literature and
Fiction</span></a></span>
    </div>
</div>

which yields

 [ a schema:WebPage;
    schema:breadcrumb ([ a schema:Breadcrumb;
        schema:name "Books";
        schema:url <category/books.html>] [ a schema:Breadcrumb;
        schema:name "Literature and Fiction";
        schema:url <category/books-literature.html>])] .


## 4. no @rel with schema:url

Finally, the previous example with explicit schema:url also works with
inline @property attributes and gives the same output:

<div vocab="http://schema.org/" typeof="WebPage">
    <div>
      <span property="breadcrumb" typeof="Breadcrumb" inlist=""><a
property="url" href="category/books.html"><span
property="name">Books</span></a></span> >
      <span property="breadcrumb" typeof="Breadcrumb" inlist=""><a
property="url" href="category/books-literature.html"><span
property="name">Literature and Fiction</span></a></span> >
    </div>
</div>


In conclusion, could you live without an explicit schema:url? It does
reduce the amount of markup quite a bit, which is quite crucial in the
context of breadcrumbs where there can be a lot of items.

Re. Egor's proposal where each child item is wrapped into its parent, I'm
not sure the HTML for that is very intuitive, I'd prefer to just have a
flat bunch of elements rather than nesting them in HTML, it's less error
prone IMO. His first argument was "Current breadcrumbs cannot be stored in
an unordered storage like JSON", but afaik, JSON can preserve order. The
second argument is about multiple breadcrumb chains, and I admit it's a
valid argument to have hierarchies of breadcrumb items in this scenario,
but is this use case very popular in the reality? could we see some
examples?

HTH,
Steph.


On Mon, Nov 12, 2012 at 1:40 PM, Gregg Kellogg <gregg@greggkellogg.net>wrote:

> On Nov 12, 2012, at 4:24 AM, Dan Brickley <danbri@danbri.org> wrote:
>
> > Dear RDFa WG,
> >
> > I'm looking for some advice on schema.org markup options. I hope to
> > join the WG shortly but wanted to start a conversation as early as
> > possible.
> >
> > Schema.org's markup for breadcrumbs is both popular and (currently)
> > broken. The issue at http://www.w3.org/2011/webschema/track/issues/10
> > gives some backstory, but factors include Microdata's rule for
> > concatenating subelements, as well as the difficulty of representing
> > ordered lists of link/label pairs as simple triples without complex
> > markup. For the purposes of this mail, I am only interested in the
> > RDFa 1.1 possibilities.
> >
> > Egor (cc:'d) has made a draft of a proposal for improving our design,
> > http://www.w3.org/wiki/WebSchemas/Breadcrumbs . This draft explores an
> > approach that makes explicit within the extracted graph, the ordering,
> > labelling and URLs from a 'breadcrumbs' section of HTML.
> >
> > I would very much like to get the RDFa WG's perspective on this issue.
>
> Well, I can give you my perspective on this issue. From a Linked Data/RDF
> perspective, I would expect to see breadcrumbs to give me an ordered list
> of links to the relevant resources, not HTML markup that has meaning only
> to a human.
>
> >From a Microdata+RDF perspective, schema:breadcrumbs is described as a
> property having an ordered list of values, so that parsing the following
> yields a list in Turtle:
>
> <div itemscope itemtype="http://schema.org/WebPage">
>     <div itemprop="breadcrumb">
>       <a href="category/books.html">Books</a> >
>       <a href="category/books-literature.html">Literature and Fiction</a> >
>       <a href="category/books-classics">Classics</a>
>     </div>
> </div>
>
> @prefix md: <http://www.w3.org/ns/md#> .
> @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
> @prefix rdfa: <http://www.w3.org/ns/rdfa#> .
> @prefix schema: <http://schema.org/> .
>
> <> md:item ([ a schema:WebPage;
>        schema:breadcrumb ("""
>       Books >
>       Literature and Fiction >
>       Classics
>     """)]);
>    rdfa:usesVocabulary schema: .
>
> The intention was for each link to be a URI in this list, so you could do
> the following, instead:
>
> <div itemscope itemtype="http://schema.org/WebPage">
>     <div>
>       <a itemprop="breadcrumb" href="category/books.html">Books</a> >
>       <a itemprop="breadcrumb"
> href="category/books-literature.html">Literature and Fiction</a> >
>       <a itemprop="breadcrumb" href="category/books-classics">Classics</a>
>     </div>
> </div>
>
> Which would give you:
>
> @prefix md: <http://www.w3.org/ns/md#> .
> @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
> @prefix rdfa: <http://www.w3.org/ns/rdfa#> .
> @prefix schema: <http://schema.org/> .
>
> <> md:item ([ a schema:WebPage;
>        schema:breadcrumb (<category/books.html>
> <category/books-literature.html> <category/books-classics>)]);
>    rdfa:usesVocabulary schema: .
>
> In RDFa 1.1 (not Lite), you can do this with @inlist and @rel:
>
> <div vocab="http://schema.org/" typeof="WebPage">
>     <div rel="breadcrumb" inlist>
>       <a  href="category/books.html">Books</a> >
>       <a href="category/books-literature.html">Literature and Fiction</a> >
>       <a href="category/books-classics">Classics</a>
>     </div>
> </div>
>
> Giving:
>
> @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
> @prefix rdfa: <http://www.w3.org/ns/rdfa#> .
> @prefix schema: <http://schema.org/> .
>
> <> rdfa:usesVocabulary schema: .
>
>  [ a schema:WebPage;
>     schema:breadcrumb (<category/books.html>
> <category/books-literature.html> <category/books-classics>)] .
>
> In RDFa 1.1 Lite, you'd need to use @property and repeat both @proprty on
> each <a>. but I don't think @inlist is officially part of RDFa 1.1 Lite.
>
> > Looking at
> http://www.w3.org/TR/2012/REC-rdfa-core-20120607/#markup-fragments-and-rdfa
> > and http://www.w3.org/TR/2012/REC-rdfa-core-20120607/#s-xml-literals
> > it seems an alternate design might be possible with RDFa. Instead of
> > trying to make the entire 'breadcrumb' structure explicit as a graph,
> > we could put the whole breadcrumb into a single property value as a
> > larger piece of markup. The current spec shows this example:
> >
> > <h2 property="dc:title" datatype="rdf:XMLLiteral">
> >  E = mc<sup>2</sup>: The Most Urgent Problem of Our Time
> > </h2>
> >
> > ...presumably this will be adjusted in the HTML+RDFa world. There was
> > discussion in the RDF WG earlier this year towards HTMLLiteral or HTML
> > as a datatype;
> http://lists.w3.org/Archives/Public/public-rdf-wg/2012May/0612.html
> > and the latest drafts now have such a datatype:
> >
> >
> http://dvcs.w3.org/hg/rdf/raw-file/default/rdf-concepts/index.html#section-html
> > http://www.w3.org/TR/2012/WD-rdf11-concepts-20120605/#section-html
> > (latest public and editor's drafts seem identical)
>
> Not a fan of this use case, but I believe that our intention is to support
> rdf:HTML in HTML+RDFa 1.1, certainly my processor does.
>
> > "5.2 The rdf:HTML Datatype
> >
> > RDF provides for HTML content as a possible literal value. This allows
> > markup in literal values. Such content is indicated in an RDF graph
> > using a literal whose datatype is a special built-in datatype
> > rdf:HTML. This datatype is defined as follows[...]"
> >
> > Let's look at the older Microdata example we still publish and
> > schema.org. Can we talk through how this might look as an HTML
> > fragment?
> >
> > First, the current example:
> >
> > <body itemscope itemtype="http://schema.org/WebPage">
> > ...
> > <div itemprop="breadcrumb">
> >  <a href="category/books.html">Books</a> >
> >  <a href="category/books-literature.html">Literature & Fiction</a> >
> >  <a href="category/books-classics">Classics</a>
> > </div> ...
> > </body>
> >
> > Now, let's put that in RDFa 1.1, with the whole markup block as the
> > value of the 'breadcrumb' property:
> >
> > <body typeof="http://schema.org/WebPage">
> > ...
> > <div property="breadcrumb" datatype="rdf:HTML">
> >  <a href="category/books.html">Books</a> >
> >  <a href="category/books-literature.html">Literature & Fiction</a> >
> >  <a href="category/books-classics">Classics</a>
> > </div> ...
> > </body>
> >
> >
> > While this meets our goal of simple markup, I see a couple of
> > potential problems. Firstly the name of the datatype looks a little
> > odd from an HTML markup perspective.  Secondly, the RDF spec requires
> > that all supporting context, declarations and base URIs be packed into
> > the markup. So the relative URIs wouldn't work.
> >
> > "Any language annotation (lang="…") or XML namespaces (xmlns) desired
> > in the HTML content must be included explicitly in the HTML literal.
> > Relative URLs in attributes such as hrefdo not have a well-defined
> > base URL and are best avoided."
> >
> > My conclusion so far is that our markup would have to be either
> >
> > A)
> > <body typeof="http://schema.org/WebPage">
> > ...
> > <div property="breadcrumb" datatype="rdf:HTML">
> >  <a href="http://example.com/category/books.html">Books</a> >
> >  <a href="http://example.com/category/books-literature.html">Literature
> > & Fiction</a> >
> >  <a href="http://example.com/category/books-classics">Classics</a>
> > </div> ...
> > </body>
> >
> > B) put base="http://example.com/" in the HTML <head>.
> >
> >> From
> http://www.w3.org/TR/2012/REC-rdfa-core-20120607/#s_curieprocessing
> > I understand that an RDFa 1.1 parser will help by resolving relative
> > URI paths, but only for the values of the core RDFa attributes. Am I
> > correct to understand that they will not rewrite rdf:HTML markup
> > blocks to make URI references absolute?
>
> URI expansion comes from HTML semantics, and works with any attributes
> that takes a URL (although it is somewhat broken for @href and @src in
> HTML5).
>
> > Apologies for the long mail, but both crawl data and schema.org site
> > logs show that breadcrumb markup is of great interest to Web
> > developers, so I would like to do everything possible to explore the
> > design space while we still have some possibility to fine-tune the
> > designs at schema.org and in the RDFa/HTML spec.
> >
> > Does the direction I sketch make sense, from an RDFa WG perspective?
> > Is there anything we can do to make the markup easier for publishers
> > and developers? Would another named markup datatype that absolute-ized
> > relative links be feasible at this stage? Did I miss any other design
> > options? Would more formal requirements analysis be useful?
>
> Another possibility would be to use BNodes for each element, with
> schema:name and schema:url, which would give you something like the
> following:
>
> @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
> @prefix rdfa: <http://www.w3.org/ns/rdfa#> .
> @prefix schema: <http://schema.org/> .
>
> <> rdfa:usesVocabulary schema: .
>
>  [ a schema:WebPage;
>     schema:breadcrumb (
>       [a schema:Breadcrumb; schema:url <category/books.html>; schema:name
> "Books" ]
>       [a schema:Breadcrumb; schema:url <category/books-literature.html>;
> schema:name "Literature" ]
>       [a schema:Breadcrumb; schema:url <category/books-classics>;
> schema:name "Classics"
>   )] .
>
> That could fallout with reasonable application of @inlist, and @typeof. It
> could work in Microdata too, with greater use of @itemscope and @itemtype.
>
> Gregg
>
> > cheers,
> >
> > Dan
> >
>
>
>


-- 
Steph.