1. 1. Leigh Dodds @ldodds http://kasabi.com Creating APIs over RDF Data Sources 8 thJune 2011. SemTech 2011
2. 2. The Trouble with SPARQL
3. 3. Try our SPARQL Endpoint! Run Query
4. 4. http://dbpedia.org/sparql?default-graph-uri=http%3A%2F%2Fdbpedia.org&query=SELECT+%3Fresult+FROM+%3Chttp%3A%2F%2Fdbpedia.org%2Fresource%2FBMW_Z8%3E+WHERE+{+%3Chttp%3A%2F%2Fdbpedia.org%2Fresource%2FBMW_Z8%3E+dbpprop%3Aname+%3Fresult+.+FILTER+%28LANG%28%3Fresult%29+%3D+%27en%27%29+.}&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. http://api.simplegeo.com/1.0/context/{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 http://api.kasabi.com/api/find-recipe-ingredient?ingredient={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 http://purl.org/linked-data/api/spec 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
    • Select
    • View
    • Request
    • Response
    • Format
    • SPARQL Endpoint
    • SELECT ?itemWHERE { }
    • Endpoint
    • DESCRIBE
    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 "10" ; api:endpoint spec:foods . spec:foods a api:ListEndpoint ; api:uriTemplate "/foods" ; api:selector [api:filter "type=Food" ]; api:defaultViewer api:describeViewer . rdf:type api:label "type" . recipe:Food api:label "Food" .
28. 28. { "format": "linked-data-api", "version": "0.2" "result": { "items": [ { "label": "Balsamic Vinegar", "isPrimaryTopicOf": "http://www.foodista.com/food/23HWFLXY "type": "http://linkedrecipes.org/schema/Food", "_about": "http://data.kasabi.com/dataset/foodista/food/23HWFLXY", "description": "Balsamic Vinegar is..." }, ... ], "modified": "Monday, 06-Jun-11 19:15:43 UTC", "itemsPerPage": 10, "startIndex": 0, "type": "http://purl.org/linked-data/api/vocab#Page", "first": "/api/foodista-linked-data-api/foods.json?_page=1", "_about": "/api/foodista-linked-data-api/foods.json?_page=1", "next": "/api/foodista-linked-data-api/foods.json?_page=2", ... }
29. 29. Open Source Implementations Puelia (PHP) http://code.google.com/p/puelia-php/ Elda (Java) http://code.google.com/p/elda/
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 SPARQLpoweredAPIs Recognise need for bridging, adapting between tools/systems/communities
33. 33. Support a view source approachEnable Crowd-Sourcing of APIs by sharing configuration & queries
34. 34. Try It For Yourself! http://beta.kasabi.com Linked Data, RDF and API hosting Demo: 9.30 tomorrow