I want to write reviews of the books I recently read. I want these reviews to be
- Open Data as CC0
- Linked Open Data
- Using schema.org
As I could not find a web app for doing this (e.g. you can’t write reviews at Open Library)
I thought to do this using my own blog. And it’s easy enough. That
is, if you ever wrote HTML by hand. It is kind of 90ties – but
then, the internet was nicer in those days (no ads, no spam, no flash,
nostalgia nonsense now). Here is how it’s done.
Using a fairly uncommon blog software named pebble
I was’nt too surprised that RDFa is not supported in any way. But the
software allows me to input HTML source blocks. And that’s all you
need to write a review using schema.org vocabulary and RDFa.
To be able to use Linked Open Data (LOD) , we need other LOD so that we can link them. I read a german edition of Lamentation by Ken Scholes
. Sadly, I wasn’t able to find that manifestation as LOD – but hey
: it is Open Library, and I can simply add the missing resource by my
own! Which I did. Thus creating “http://openlibrary.org/books/OL25430867M” (btw I added the “about the book” description and some tags at the work level of the manifestation.)
Why RDFa and not microdata ?
How to ?
I inserted the following HTML fragment:
<div vocab="http://schema.org/" typeof="WebPage Review" about="http://www.dr0i.de/lib/2013/09/14/ken_scholes_sndenfall.html">
This is a review about
<a property="itemReviewed" href="http://openlibrary.org/books/OL25430867M/">
'Ken Scholes: Lamentation'.
stars. Written by
<a property="author" href="http://lobid.org/person/pc">
<span content="2013-09-14" property="publishDate">
on September 2013
<span property="reviewBody" xml:lang="en">
The setting of the book .... blah ... reminds me of
<a property="citation" href="http://viaf.org/viaf/52700">
... it should not be recommended by
<a href="http://libraryjournal.com/" property="citation" >
The first line is necessary to indicate that the schema.org
vocabulary is used and that’s a webpage with one review. The review is
explicitly given the URI using “about” – so this becomes the “subject”
of the triples.
This is not needed, because as default the URI of the webpage of the review is taken – and they are the same.
(There may occur situations when you need to distinct between the thing
you want to talk about and the thing you talk with , e.g. providing
metadata for an other webpage or non-webpage , or having a list of
reviews where each review has it’s own website (to be able to make
statements about each single review.))
You can understand the HTML fragment above on your own if you
lookup the URIs : suffix the value of the “property” attribute to the
vocab url “http://schema.org/”, thus e.g. you get “http://schema.org/reviewBody”
. The HTML attribute “property” can be used in HTML tags: you may use
the link tag “<a>” when you link something or the “<span>”
tag if you just want make literal statements. Having literals it makes
sense to give them language tags, e.g. ‘xml:lang=”en”‘.
Now, have a look at http://www.dr0i.de/lib/2013/09/14/ken_scholes_sndenfall.html to see how it renders for you. And what does a machine see, say google? Let us use a tool from the W3C, the “Distiller”, showing us the turtle notation of the underlying RDF:
@prefix cc: <http://creativecommons.org/ns#> .
@prefix dc: <http://purl.org/dc/terms/> .
@prefix rdfa: <http://www.w3.org/ns/rdfa#> .
@prefix schema: <http://schema.org/> .
<http://www.dr0i.de:80/lib/> cc:license <http://creativecommons.org/publicdomain/zero/1.0/>;
rdfa:usesVocabulary schema: .
<http://www.dr0i.de/lib/2013/09/14/ken_scholes_sndenfall.html> a schema:Review, schema:WebPage;
schema:reviewBody "The setting ..."@en;
Nice and clearly structured, semantics all clear, isn’t it ? If you think so – you are probably a machine ! 0110100001101001 !
Btw, of course you are allowed to use RDFa anywhere in your webpage.
Pebble uses an info box about the blog on the upper right side, and
nothing prevents you from pasting some HTML in there. We have tow
statements here about the whole blog: 1. the license of the content and
2. the author of the blog .
Now, I am not totally happy with that. For me, it is not the writing
of RDFa and HTML by hand, but that the source of the webpage looks
something like a mess and it is not really valid RDFa in HTML. Rapper, a
nice tool for working with RDF, rejects the parsing of the RDFa in this
webpage. But by using Distiller, we can get the RDF even by command
line (and remember: Distiller is coming from the W3C, so this RDFa is
“valid enough” to serve it’s purpose):
$ curl http://www.w3.org/2012/pyRdfa/extract?uri=http://www.dr0i.de/lib/2013/09/14/ken_scholes_sndenfall.html
So this is good enough for me. I will go on writing book reviews
using the template above. For more information, examples and tutorials
see http://schema.rdfs.org (yes, the site is a little bit outdated, but none the less helpful, since the schema.org examples still only shows microdata, (you can see with a glimpse that it is microdata when the “itemprop” attribute is used instead of “property”)), even if microdata may be discontinued.