Unraveling Linked Data: The Semantic Chaos

1. Linked data the next network?

2. Eh? This linked data thing, I don’t get it. The idea behind the Semantic Web is that the current web of documents is difficult for computers to process, because it’s all unstructured information. A web of data would be more like a database: more computationally accessible than a bunch of documents.

3. Eh? Okay, let’s watch this funny video. The Story of Web 3.0

4. Basics: URIs and RDF Linked data is the expression of the basic Semantic Web technologies. It is “open” in the sense of being freely available for anyone to use for anything. 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).

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

6. Linked data examples Here are some examples of data sets available as linked data in RDF: The AGROVOC thesaurus (term: maize)  Library of Congress Subject Headings (heading: school sports: fiction) Amsterdam museum objects

7. But...why? Why would cultural heritage institutions care? Here’s what some people say: Europeana Biodiversity heritage library

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

9. But...why? In addition to resource discovery, linked data can enable the development of applications that enable different sorts of data manipulation—from data curation to document creation, if you will. Viewshare (Recollection) Visualizing Emancipation

10. 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.

11. 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.

12. 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?

13. Linked data = semantic chaos?

14. Linked data = semantic chaos? Let’s look at the aggregated linked data associated with Michael Jackson and Barack Obama. Sig.ma linked data synthesis engine

15. Linked data = semantic chaos? When do such semantic conflicts matter, and how do they matter? After all, we know there’s variation in how library subject headings are applied, and while that’s not ideal, it’s not going to crash an airplane, either.

16. Wait, did you say recipes? Does Google’s Recipe View use linked data? No! Google (and Yahoo and Bing) has implemented its own semantic markup, using “microdata” that’s integrated within a Web page. Read about it at schema.org. This approach can be made to work with linked data.