Linked Data and the Digital Public Space

Presentation at the Kultivate Linked Data Workshop at HEFCE in London on Monday 12th December 2011. See http://pres.spindle.org.uk/2011/kultivate/ for more information.

Transcript

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2. You can find slides, notes and example data at: http://bit.ly/dpskultivate or http://pres.spindle.org.uk/2011/kultivate/
3. Part 1: What’s in a name?
4. Identifiers • All very important, everybody knows that • The great thing about identifiers is that there are so many of them…
5. URIs • URIs have some unique properties • Anybody can make them • They can refer to anything • A (significant) subset of URIs are resolveable
6. Resolvable URIs are useful The Linked Data golden rule: • Give everything a URI and publish the data about that thing at that URI
7. What makes a good Linked Data URI? • It uses http: or https: — you want things to be able to consume your data, right? • It differentiates between “documents” and “things described by those documents” • It’s not going to change • It’s the same place humans go for a page about that thing
8. The pattern http://example.com/catalogue/AB12458#thing Your server The largest collection you have containing the item (in this case, “our catalogue of everything”) Your persistent identifier The fragment identifier
9. The fragment identifier? • A cheap (but elegant) hack to avoid ambiguity • Allows differentiation between “resources” and “things described by resources” • Lots of common properties can be used to describe either the document or the thing • It doesn’t really matter what you pick as your fragment identifier
10. Part 2: A step-by-step guide to publishing some Linked Data with just a text editor and a Web server (or: “Look Ma, no database!”)
11. Our example scenario • It’s data about a book (Should be familiar territory for many of you) • We’ve got our own internal, stable, catalogue reference — in our case a UUID, but the exact nature isn’t too important • We’ve got a web server to publish it on
12. What we’re asserting • The book’s ISBN • The book’s title and author • Some links to other sources of information about this book
13. It looks like this: 52279a4d-1707-45e7-b19d-f5571218e9dd ISBN-13: 978-1899066100 Title: Acronyms & synonyms in medical imaging Author: David Allison More information can be found at: http://bnb.data.bl.uk/id/resource/011012558
14. Our identifier • The prefix (where we’re going to put it all): http://foobarbooks.org/items/ • Our local identifier (our catalogue reference): 52279a4d-1707-45e7-b19d-f5571218e9dd • The fragment (which differentiates information about the book): #item
15. Our identifier • Putting it all together: http://foobarbooks.org/items/52279a4d-1707-45e7-b19d-f5571218e9dd#item • This pattern would work for any kind of item
16. Publishing the data • We’ll start with the human-readable version • Let’s create 52279a4d-1707-45e7-b19d- f5571218e9dd.html • Nothing particularly out of the ordinary here!
17. What happens when you resolve the URI? 1. You type… http://foobarbooks.org/items/52279a4d-1707-45e7-b19d-f5571218e9dd#item …into your address bar 2. Your browser requests… /items/52279a4d-1707-45e7-b19d-f5571218e9dd …from the server at foobarbooks.org on TCP/IP port 80 (that’s where HTTP lives)
18. Requesting the document The request looks something like this: GET /items/52279a4d-1707-45e7-b19d-f5571218e9dd HTTP/1.0 Host: foobarbooks.org Accept: text/html;q=1.0, text/xml;q=0.7, application/xml;q=0.8 Accept-Language: en-GB, en-US;q=0.9, en;q=0.7 User-Agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10_7_2; en- GB) AppleWebKit/534.51.22 (KHTML, like Gecko) Version/534.51.22 Safari/533.21.1
19. And then…? 3. The server sends back a 404 Not Found response because there’s no document named /items/52279a4d-1707-45e7-b19d-f5571218e9dd 4. Oh :(
20. Cool URIs don’t change • We could change our identifier to explicitly include the “.html” • “.cgi, or even .html, is something which will change. You may not be using HTML for that page in 20 years time, but you might want today's links to it to still be valid.” • Why not just configure the server to not need the filename extension?
21. Enter mod_negotiation $ cat .htaccess Options +MultiViews $
22. Let’s try that request again… 3. The server sends back the HTML document that we created. 4. Hurrah!
23. Big deal • So far, we’ve assigned a URI, created a human-readable document and published it on a Web server. • Welcome to 1992.
24. Adding some structured data • We can describe our book using RDF • RDF is useful because it identifies everything using URIs, even the classes and properties • This means that (a) anybody can play, and (b) there’s not much risk of conflict
25. Publishing our RDF • Start with RDF/XML • Many people find it ugly, but it’s the one RDF serialisation everything can process • So, we’ll create 52279a4d-1707-45e7-b19d- f5571218e9dd.rdf • This is why putting .html into our item URI would be problematic — without special knowledge, consumers would only retrieve the HTML document!
26. What happens now? • When a human requests the item from the Web server nothing changes. They still get the HTML. • When a piece of software which understands RDF/XML requests it, though…
27. Requesting the RDF The request looks something like this: GET /items/52279a4d-1707-45e7-b19d-f5571218e9dd HTTP/1.0 Host: foobarbooks.org Accept: application/rdf+xml, text/turtle, application/json User-Agent: MyLinkedDataProcessor/1.0 And the response: HTTP/1.0 200 OK Content-Type: application/rdf+xml Content-Location: /items/52279a4d-1707-45e7-b19d-f5571218e9dd.rdf <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns"> : :
28. What can you do now? • You could add structured data to the HTML document which would mean some consumers don’t have to request the RDF/ XML • You could help consumers which don’t understand Content Negotiation by adding a <link> element to your HTML • You could publish data in other formats: JSON, Turtle, CSV, MARC…
29. Part 3: Digital Public Space at the BBC
30. The BBC Archive: •2.3m hours of film & video •300,000 hours of audio •4m photographs •20,000 rolls of microfilm
31. What are we doing? • Taking lots of that lovely Linked Data • Caching it (to make it easier for consuming applications) • Breaking it down into people, places, events, collections and… things • Finding the overlaps
32. (Arrows not intended to be representative)
33. Catalogue Catalogue dbpedialite LCSH Asset store Asset store
34. Catalogue Catalogue Aggregator
35. thing one thing two ?
36. Two ways of finding overlaps • The easy way: explicit links between catalogues in their data (the “Linked” part of “Linked Data”) • The harder, but more common way: heuristic matching
37. Stub object “George Orwell” “मो#तहारी” dbo:BirthPlace Person skos:exactM atch rdf:type Stub object dbo:BirthPlace skos:exactMatch
38. What do you get? • Linked Data In, Linked Data Out • (Sometimes) Garbage In, Garbage Out • A “Webby” platform for exploration of cultural archives
39. A stub, pointing at the source data
40. Status • We’ve got a prototype aggregator • We built a couple of interfaces, and commissioned a third party to build another • We threw a small subset (500k items) at it
42. What’s next? • Put a lot more data in and let the matching code do its thing • Make as much as we can available to as many people as possible