Creating APIs over RDF


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Creating APIs over RDF

  1. 1. Leigh Dodds @ldodds Creating APIs over RDF Data Sources 8 th June 2011. SemTech 2011
  2. 2. The Trouble with SPARQL
  3. 3. Try our SPARQL Endpoint! Run Query
  4. 4.{}&debug=on&timeout=&format=text%2Fhtml&save=display&fname= Trial and error experiments aren't easy
  5. 5. APIs have Affordance They're like pulling a thread The URLs unravel into useful data
  6. 6.{lat},{lon}.json Trial and error experiments are easy
  7. 7. SPARQL is for Power Users
  8. 8. How can we give RDF datasets more affordance?
  9. 9. Linked Data? Typically not expressive enough to support all useful interactions Expensive to materialize all useful data partitions E.g. by date-time, location, top ranking, etc
  10. 10. Build Custom APIs? Write custom code against your graph store Can be expensive to build & maintain Undermines power of web of data
  11. 11. OData? Standard data API from Microsoft Very similar to RDF & Linked Data approach Can be implemented over SPARQL endpoint
  12. 12. SPARQL Stored Procedures & The Linked Data API
  13. 13. SPARQL “Stored Procedures”
  14. 14. Bind SPARQL query to a URL{x}
  15. 15. More than just a URL shortener 1. Identify query bound to URL 2. Inject parameters from URL & config 3. Apply paging/sorting options 4. Execute query 5. Optionally, apply post-processing transformations
  16. 16. Parameter Passing Optional and Required Parameters Mapping to a particular type of RDF Term, e.g. literal, URI May have a default value May have a default prefix, e.g. base URL
  17. 17. Post-Processing Named transformations that generate a specific mime-type Supports generating custom output formats Currently just XSLT. Could support JS
  18. 18. Stored Procedure Benefits Declarative approach Offers simpler interface to developers Retains RDF output, but supports custom formats
  19. 19. The Linked Data API
  20. 20. Linked Data API Jeni Tennison (TSO), Dave Reynolds (Epimorphics), Leigh Dodds
  21. 21. Linked Data API Map parameterised URLs to graph queries to extract data views
  22. 22. Linked Data API Optimize for common query patterns Prioritize simple RESTful interactions not complex queries Provide pathway to exploring RDF and SPARQL
  23. 23. Processing Model <ul>Select </ul><ul>View </ul><ul>Request </ul><ul>Response </ul><ul>Format </ul><ul>SPARQL Endpoint </ul><ul>SELECT ?item WHERE { … } </ul><ul>Endpoint </ul><ul>DESCRIBE <x> <y> </ul>API Config
  24. 24. Selecting Resources URL mapped to query patterns by API configuration Query variables injected from URL path or query string Simple path expressions for traversing graph Support for sorting and paging
  25. 25. Viewing Resources Default “view” is Concise Bounded Description Can specify arbitrary collections of properties in config or URL
  26. 26. Output Formats Simple JSON and XML formats Standard RDF serializations Custom formats, including HTML, via XSLT
  27. 27. @prefix spec: <> . @prefix api: <> . @prefix rdf: <> . @prefix rdfs: <> . @prefix recipe: <> . spec:api a api:API ; api:defaultPageSize &quot;10&quot; ; api:endpoint spec:foods . spec:foods a api:ListEndpoint ; api:uriTemplate &quot;/foods&quot; ; api:selector [ api:filter &quot;type=Food&quot; ]; api:defaultViewer api:describeViewer . rdf:type api:label &quot;type&quot; . recipe:Food api:label &quot;Food&quot; .
  28. 28. { &quot;format&quot;: &quot;linked-data-api&quot;, &quot;version&quot;: &quot;0.2&quot; &quot;result&quot;: { &quot;items&quot;: [ { &quot;label&quot;: &quot;Balsamic Vinegar&quot;, &quot;isPrimaryTopicOf&quot;: &quot; &quot;type&quot;: &quot;;, &quot;_about&quot;: &quot;;, &quot;description&quot;: &quot;Balsamic Vinegar is...&quot; }, ... ], &quot;modified&quot;: &quot;Monday, 06-Jun-11 19:15:43 UTC&quot;, &quot;itemsPerPage&quot;: 10, &quot;startIndex&quot;: 0, &quot;type&quot;: &quot;;, &quot;first&quot;: &quot;/api/foodista-linked-data-api/foods.json?_page=1&quot;, &quot;_about&quot;: &quot;/api/foodista-linked-data-api/foods.json?_page=1&quot;, &quot;next&quot;: &quot;/api/foodista-linked-data-api/foods.json?_page=2&quot;, ... }
  29. 29. Open Source Implementations Puelia (PHP) Elda (Java)
  30. 30. Linked Data API Summary Declarative configuration-driven approach More sophisticated than SSPs Integrates well with Linked Data publishing Slightly higher learning curve
  31. 31. Summary
  32. 32. Adopt hybrid approach to encourage adoption Combine Linked Data with SPARQL powered APIs Recognise need for bridging, adapting between tools/systems/communities
  33. 33. Support a “view source” approach Enable Crowd-Sourcing of APIs by sharing configuration & queries
  34. 34. Try It For Yourself! Linked Data, RDF and API hosting Demo: 9.30 tomorrow