LDOW2011 slides

1. RESTful writable APIs
for the web of Linked
Data using relational
storage solutions
Antonio Garrote
María N.Moreno García

2. Outline
1. Introduction
2. SPARQL to SQL mapping using R2RML
3. RESTful API
4. Conclusions

3. Web APIs
OAuth
Key Value
Mobile App. Store
HTTP
API
JS. App JSON MVC
Native App.
Dynamic Relational
Web App. DB

4. Linked data APIs?
• RDF data model vs JSON objects
• Object IDs vs URIs
• Properties identified by URIs vs plain
strings
• URIs linking data in different services

5. Transition path
• Translation of SPARQL update queries into
SQL queries
• RDF graphs encoded in JSON objects
• RESTful protocol to manipulate RDF graphs

6. SPARQL to SQL
translation
• R2RML starting point
Relational
RDF quads TableMappings
Data
R2RML
Document

7. SPARQL to SQL
translation
• inverse transformation
R2RML
Document
SPARQL
Query
QuadPatterns QuadMatchers SQL

8. SPARQL to SQL
translation
Constant
Mappings
R2RML
Mapping
(Table, Subject, Property, Object, Graph)
Variable
Mappings
Quad Matchers

9. SPARQL to SQL
translation
(Table, Subject, Property, Object, Graph)
Constant
Terms
Compatible? SPARQL
Quad Pattern
Variables
+BNode IDs

10. SPARQL to SQL
translation
SELECT SPARQL
Quad Pattern
Quad Quad Quad
Matcher Matcher Matcher
σπ σπ σπ
∪ ∪
SPARQL Relational Algebra

11. SPARQL to SQL
translation
Insert SPARQL
Quad Pattern
Quad Quad Quad
Matcher Matcher Matcher
Min. Insertion Cost metric
Insert / Update SQL DM Query

12. SPARQL to SQL
translation
• Different compatibility functions: data types,
language tags in literals
• R2RML extensions to generate IDs from
URIs
• Limitations: auto increment columns and
database constraints

13. RESTful API
• Starting point: “SPARQL 1.1 Uniform HTTP
Protocol for Managing RDF graphs”
• Granularity: RDF named graph
• HTTP uniform interface semantics

14. RESTful API
• Declarative definition of APIs (RDFS
vocabulary)
- URI templates
- Mapping of templates to SPARQL
endpoints

15. RESTful API
• Minting of resource URIs
HTTP POST Request HTTP GET Response
graph_uri
[
<p1> <o1> ;
<uri> graph_uri#self
<p1> <o1> ;
<p2> <o2>;
<p2> <o2>;
...
...
]
RDF RDF
200
201
New resource URI

16. RESTful API
• Extensions (linked-data-api):
- JSON-LD as the primary media type
- Method overloading
- JSONP support
- Format URL parameter
- Pagination parameters

17. Sample Application
• Library
• Prototype
- JavaScript client
- RESTful API
- FOAF+SSL auth
- Relational backend
http://github.com/antoniogarrote/clj-r2rml
http://antoniogarrote.com/cvbuilder

18. Conclusions
• Linked data and sem. web technologies can
help us to build better web APIs
• Huge opportunity to increase the amount
of linked data available in the web
• Real benefits for end users
• Easy transition path for web developers
must be provided