1. Linked data the next network?

2. The Web of documents is for people The Web of data is for computers The Web of documents is difficult for computers to process, because it’s all unstructured information. (Remember last week and retrieval? Web search is so imprecise!) A Web of data would be more like a database: more computationally accessible than a bunch of documents.

3. Basics: URIs and RDF Linked data relies on just a few basic elements: Unique identifiers (URIs, of which the URL is a subset) to distinguish entities, properties, and relations (things and concepts). RDF, the Resource Description Framework, a way to describe the world through the expression of triples (subjects, predicates, and objects).

4. Basics: URIs and RDF RDF triples are modeled as nodes and arcs in a graph. Here is an example from the W3C RDF Primer:

5. Basics: links Vocabularies can be linked together, enabling computers to make inferences about different datasets: Diagram from Dunsire, Hillmann, and Phipps, 2012

6. Basics: links An example of such inferencing (dashed lines are inferences): Diagram from Dunsire, Hillmann, and Phipps, 2012

7. Linked data examples Here are some examples of data sets available as linked data in RDF: A metadata schema: Dublin Core A vocabulary to use with a metadata schema: Library of Congress Subject Headings (heading: school sports: fiction) Cultural heritage metadata: Amsterdam Museum (via DataHub) Government data: Data.gov RDF datasets

8. But...why? Why would anyone care about publishing or using linked data, especially cultural heritage institutions? Here’s what the folks at Europeana have to say: Europeana’s pitch for linked open data

9. But...why? So, resource discovery is one reason. Dear Semantic Web, where in the world are all of Giorgio Morandi’s paintings located? —— Thanks, Melanie Dear Melanie, here is the information you asked for. —Love, Semantic Web

10. But...why? Right now, large-scale cultural heritage aggregators serve as unified search portals for cultural heritage data (er, metadata, er, ack): Europeana Digital Public Library of America

11. But...why? Applications can manipulate this open data in different ways—generating new kinds of value from cultural heritage objects (and from digital representations of those objects, and their descriptive metadata, or data derived from them). DPLA apps Europeana exhibits Out of the Trenches (Libraries and Archives Canada) Out of the Trenches (Libraries and Archives Canada)

12. What was that about the neat people and the sloppy people? This is where the “linked data” people deviate from the “ontology” people, and the “Semantic Web” name becomes an issue. An ontology, or set of classes, relationships, and constraints on data, enables reliable inferencing. It is great! Except complicated. For many people, way too complicated.

13. Linked data = semantic chaos? Its simplicity makes linked data easy to generate and disseminate. Unlike “real” ontologies. However, with this simplicity comes the potential for semantic conflict, when the same object (as referenced with the same URI) is described in conflicting ways, or when the same property (as referenced with the same URI) is used in different ways to describe different objects.

14. Linked data = semantic chaos? Is it correct to say that Amy Winehouse and Diana Ross are both members of the Jazz genre? Does this align with our sense of either artist, or with our sense of jazz? Or...does that kind of statement make sense at all? Can a person be associated with a genre, or just a work?

15. Linked data = semantic chaos?

16. What does “still life” mean? Is this semantic variability problematic? DPLA (subject = “still lifes”) Europeana (subject = “still lifes”)

17. Linked data = semantic chaos? Is Woody Allen an “American jazz clarinetist”?“American jazz clarinetist”? I mean, I guess so...but...

18. Linked data = semantic chaos? We know that such semantic variability is inevitable. But when and how does it matter? What should publishers, curators, re-publishers and users of datasets do?