1. Paths towards the Sustainable Consumption of Semantic Data on the Web Aidan Hogan & Claudio Gutierrez

2. Growth of the Linked Data Cloud Oct. 2007

3. Growth of the Linked Data Cloud Oct. 2007 Nov. 2007 Oct. 2007 Nov. 2007

4. Growth of the Linked Data Cloud Oct. 2007 Nov. 2007 Feb. 2008 Oct. 2007 Nov. 2007 Feb. 2008

5. Growth of the Linked Data Cloud Oct. 2007 Nov. 2007 Feb. 2008 Sep. 2008 Oct. 2007 Nov. 2007 Feb. 2008 Sep. 2008

6. Growth of the Linked Data Cloud Oct. 2007 Nov. 2007 Feb. 2008 Sep. 2008 Mar. 2009 Oct. 2007 Nov. 2007 Feb. 2008 Sep. 2008 Mar. 2009

7. Growth of the Linked Data Cloud Oct. 2007 Nov. 2007 Feb. 2008 Sep. 2008 Mar. 2009 July 2009 Oct. 2007 Nov. 2007 Feb. 2008 Sep. 2008 Mar. 2009 July 2009

8. Growth of the Linked Data Cloud Oct 2007 Oct. 2007 Nov. 2007 Feb. 2008 Sep. 2008 Mar. 2009 July 2009 Sept. 2010 Oct. 2007 Nov. 2007 Feb. 2008 Sep. 2008 Mar. 2009 July 2009 Sept. 2010

9. Growth of the Linked Data Cloud Oct. 2007 Nov. 2007 Feb. 2008 Sep. 2008 Mar. 2009 July 2009 Sept. 2010 Sept. 2011 Oct. 2007 Nov. 2007 Feb. 2008 Sep. 2008 Mar. 2009 July 2009 Sept. 2010 Sept. 2011

10. Growth of the Linked Data Cloud Oct. 2007 Nov. 2007 Feb. 2008 Sep. 2008 Mar. 2009 July 2009 Sept. 2010 Sept. 2011 Sept. 2012 Oct. 2007 Nov. 2007 Feb. 2008 Sep. 2008 Mar. 2009 July 2009 Sept. 2010 Sept. 2011 Sept. 2012

11. Growth of the Linked Data Cloud Oct. 2007 Nov. 2007 Feb. 2008 Sep. 2008 Mar. 2009 July 2009 Sept. 2010 Sept. 2011 Sept. 2012 Sept. 2013 Oct. 2007 Nov. 2007 Feb. 2008 Sep. 2008 Mar. 2009 July 2009 Sept. 2010 Sept. 2011 Sept. 2012 Sept. 2013

12. Growth of the Linked Data Cloud Oct. 2007 Nov. 2007 Feb. 2008 Sep. 2008 Mar. 2009 July 2009 Sept. 2010 Sept. 2011 Sept. 2012 Sept. 2013 June 2014 Oct. 2007 Nov. 2007 Feb. 2008 Sep. 2008 Mar. 2009 July 2009 Sept. 2010 Sept. 2011 Sept. 2012 Sept. 2013 June 2014

13. Growth of the Linked Data Cloud One new dataset in the past year

14. In loving memory of Linked Data 2007–2012 Survived by its research community

15. Access Methods Client has a request/query Q Server has a dataset D Client issues Q to server Server computes and returns response Q(D) D HTTP Q Q(D)

16. Access Methods Q Q D D D Q Multiple clients / multiple servers (blurred) Remote, decentralised, uncoordinated Web scale Anything else like this? Q D

17. Access Methods (over the web) “The Web is not a database” -- Alberto Mendelzon, slides from a presentation at the Workshop on Internet Data Management, Washington, November 1998.

18. Linked Data Access Methods 1.Dereferencing: – Look up a URI, get an RDF document 2.Dumps: – Get all data in an archive 3.SPARQL Queries: – Send a query, get the answers

19. DEREFERENCING

20. Dereferencing (what is it?) Q = “http://dbpedia.org/resource/Columbia” Q(D) =

21. Dereferencing (what’s wrong with it?) Responses vary from server to server – local triples where URI is subject (83%) vs. – local triples where URI is subject or object (55%) [Hogan et al. 2012] W ELL - DEFINED : For a given Q and D, clients and servers agree on what Q(D) should be.

22. Dereferencing (what’s wrong with it?) Very coarse: – Give me all capitals of South American countries. Dereference documents for all country URIs See which ones are in South America, throw away rest Throw away triples other than capitals G RANULAR : The language for Q allows the client to be specific so as to avoid wasting bandwidth

23. Dereferencing (what’s wrong with it?) No pagination: – Give me some information about Italy. Load document with 100,000 triples Throw away 99,900 triples the user won’t read P AGINATION : A large response Q(D) can be split into chunks

24. DUMPS

25. Dumps (what are they?)

26. Dumps (what’s wrong with them?) 15× compression for RDF achievable But same weaknesses as for deref. still apply [Fernández et al. 2012]

27. Dumps (what’s wrong with them?) 15× compression for RDF achievable But same weaknesses as for deref. still apply Also, no standard access methods: – Various compressions and formats – Linked through generic HTML [Fernández et al. 2012] A CCESSIBLE : The protocol and formats are defined for automatic access by software agents

28. SPARQL

29. SPARQL (what is it?) “What’s the name of the query language again … what’s that? Oh yes, SPARQL.” -- C. Mohan, June 2014, Cartagena, AMW Summer School

30. SPARQL (what is it?) Q = Q(D) = PREFIX dbo:... SELECT ?capital WHERE { ?s a dbo:Country ; dbp:capital ?c ; dcterms:subject category:Countries_in_South_America. ?c rdfs:label ?capital. FILTER (lang(?capital)="en") } PREFIX dbo:... SELECT ?capital WHERE { ?s a dbo:Country ; dbp:capital ?c ; dcterms:subject category:Countries_in_South_America. ?c rdfs:label ?capital. FILTER (lang(?capital)="en") }

31. SPARQL (to the rescue?)

32. SPARQL (what’s wrong with it?) [Buil Aranda et al. 2012]

33. SPARQL (what’s wrong with it?) [Buil Aranda et al. 2012]

34. SPARQL (what’s wrong with it?) Simple Protocol and RDF Query Language SPARQL evaluation: PS PACE -complete SPARQL 1.1 even more complex [Perez et al. 2009] [Arenas et al. 2013]

35. SPARQL (what’s wrong with it?) C OSTABLE : The cost of processing a query can be anticipated before actual processing. C ACHEABLE : Common requests can be cached and re-used. Queries can be anticipated.

36. SPARQL (what’s wrong with it?)

38. Simple Protocol And RDF Query Language Protocol always expects a perfect answer – No support for partial results, timeouts, exception handling, pagination … R OBUST : Access method can gracefully handle error cases and provide Quality of Service

39. SPARQL (what’s wrong with it?) D is a black-box for the user

40. SPARQL (what’s wrong with it?) Q = Q(D) = PREFIX dbo: SELECT (COUNT(?c) as ?count) WHERE { ?c a dbo:Country. } PREFIX dbo: SELECT (COUNT(?c) as ?count) WHERE { ?c a dbo:Country. } T RANSPARENT : The client can determine if a dataset D is relevant and the service sufficient.

41. WRAP-UP

42. Problem Categories 1.Standardised 2.Bandwidth-efficient 3.Server-processing-efficient 4.Usable by client

43. Conclusion Data access methods crucial – Access = Protocol + Query Language But current ones don’t work → need something else (or multiple things?) – Open question: