Schema.org/VisualArtwork - A series of 3 posts: post 3 of 3.
Linked Open Data
In this post I want to get a bit more technical and introduce the concept of Linked Open Data.
Linked Open Data is a way of publishing structured data that allows metadata to be connected and enriched, so that different representations of the same content can be found, and links made between related resources.
The Europeana Foundation.
A current trend in managing art information is to increasingly make data about art, architecture, and cultural heritage objects available as Linked Open Data (LOD). This applies to the information directly describing the objects, but also to the vocabularies used in the description.
The Getty Research Institute.
For the purposes of this post I’ll be looking at the final part of that second quotation: using Linked Open Data to enrich and connect the vocabularies used to describe a piece of artwork using schema.org/VisualArtwork, and specifically to use the Art & Architecture Thesaurus® published by the Getty Research Institute to provide machine-readable properties for the artform, material(s), and surface of a piece of artwork.
The basic HTML and RDFa
Here’s a simple example of the basic use of schema.org/VisualArtwork that we’ll use. I’m using RDFa in this example, but Microdata or JSON work just as well:
<div typeof="VisualArtwork"> <h1 property="name">Untitled Drawing</h1> <img property="image" src="example.org/mydrawing.jpg" alt="A scan of Untitled Drawing" /> <p> <span property="artMedium">Pencil</span> on <span property="artworkSurface">cartridge paper</span>. </p> <p> <span property="artform">Drawing</span>, <span property="dateCreated">2014</span>. </p> </div>
We’ll be concentrating on three properties where we can use the concepts of Linked Open Data to unambiguously describe the artform (medium), materials, and surface of the artwork in such a way that a piece of software can “understand” exactly what you’re describing about your artwork.
Now it gets confusing (for machines)
<span property="artMedium">Pencil</span> probably seems fairly clear and obvious to most readers of this blog, that’s because you’re (a) human, and (b) probably have a good understanding of the English language (otherwise you wouldn’t have read this far). I could alternatively have used
<span property="artMedium">Graphite pencil</span> or
<span property="artMedium">Graphite</span> and you’d probably know that I meant the same thing, but to a piece of software “Pencil”, “Graphite Pencil”, and “Graphite” are three different values: software doesn’t (usually) have the capability to understand that they’re different terms that mean the same thing.
What if I was a French artist, and I marked it up like this
<span property="artMedium">Crayon</span>? “Crayon” is French for “Pencil”, but crayon in English is a wax pastel typically used by children, not a graphite pencil at all. Immediately everything is confused!
Using Linked Open Data to remove the confusion
The Art & Architecture Thesaurus® (AAT) published by the Getty Research Institute is a controlled vocabulary that works across any language to unambiguously define a material, surface, or artform. More recently the Getty AAT has been released and formatted for use as Linked Open Data.
Here’s the amended markup:
<div typeof="VisualArtwork"> <h1 property="name">Untitled Drawing</h1> <img property="image" src="example.org/mydrawing.jpg" alt="A scan of Untitled Drawing" /> <p> <a property="artMedium" href="http://vocab.getty.edu/aat/300022443">Pencil</a> on <a property="artworkSurface" href="http://vocab.getty.edu/aat/300014136">cartridge paper</a>. </p> <p> <a property="artform" href="http://vocab.getty.edu/aat/300054196">Drawing</a>, <span property="dateCreated">2014</span>. </p> </div>
Note: if you don’t want to visibly link to the Getty URIs on your web page (they would be a bit confusing for normal visitors coming to browse—and hopefully buy—your artwork!) then you can always use
<span> elements with the RDFa
<span property="artMedium" resource="http://vocab.getty.edu/aat/300022443">Pencil</span>
Anyway, as you can see, the elements describing the material, surface, and artform now reference URIs, although the text (“Pencil”, “cartridge paper”, “Drawing”) is still there for humans like us to read.
The links point to URIs on vocab.getty.edu that are part of its structured data, and the specific links point to the URIs that unambiguously describe “Pencil”, “cartridge paper”, and “Drawing”.
I could change the language of the text in my mark-up into French (“Crayon”, “papier à cartouche”, “Dessin”) but the links would still point to the same URIs which allow software to know exactly what I mean:
<div typeof="VisualArtwork"> <h1 property="name">Dessin sans titre</h1> <img property="image" src="example.org/mydrawing.jpg" alt="un scan de mon dessin" /> <p> <a property="artMedium" href="http://vocab.getty.edu/aat/300022443">Crayon</a> sur <a property="artworkSurface" href="http://vocab.getty.edu/aat/300014136">papier à cartouche</a>. </p> <p> <a property="artform" href="http://vocab.getty.edu/aat/300054196">Dessin</a>, <span property="dateCreated">2014</span>. </p> </div>
Apologies to any French readers for my terrible French!
Thanks to Niklas Lindström and Karen Coyle for their debate and suggestions on the Public Vocabs mailing list that led to the possibility of using Linked Open Data in schema.org/VisualArtwork.
Bibliography and further reading:
Harpring, P. (2010). Introduction to controlled vocabularies: Terminology for art, architecture, and other cultural works. Los Angeles, CA: Getty Publications.
Heath, T., & Bizer, C. (2011). Linked data evolving the web into a global data space. San Rafael, CA: Morgan & Claypool.
Miller, S. (2011). Metadata for digital collections: A how-to-do-it manual. New York, NY: Neal-Schuman.
Alexiev, V., Cobb, J., Garcia, G., & Harpring, P. (2014, August). Getty Vocabularies Linked Open Data: Semantic Representation, 2.0 edition. Retrieved February, 2015, from http://vocab.getty.edu/doc/.
Other posts in this series
Schema.org/VisualArtwork - A series of 3 posts: post 3 of 3:
- Schema.org’s VisualArtwork launched
- Mapping existing data stored in VRA Core 4 format to schema.org’s VisualArtwork
- Getty AAT Linked Open Data in schema.org’s VisualArtwork