OBA: An Ontology-Based Framework for Creating REST APIs for Knowledge Graphs

1. Information Sciences Institute OBA: An Ontology-Based Framework for Creating REST APIs for Knowledge Graphs Daniel Garijo and Maximiliano Osorio {dgarijo,mosorio}@isi.edu @dgarijov, @SirSpock

2. Information Sciences Institute Exploring a SPARQL endpoint LOV https://lists.w3.org/Archives/Public/semantic-web/2015Jan/0087.html W3C Semantic Web lists (2015) Get all classes Get documentation and examples Get all classes and properties Luca Matteis Thomas Francart Jerven Bolleman

3. Information Sciences Institute Requirements for KG consumption LOV https://lod-cloud.net/#diagram SPARQL endpoint Ontology/vocabulary Documentation/ examples Developer

4. Information Sciences Institute The gap between KG engineers and consumers Ontology/KG engineer - Familiar with ontologies/vocabularies used to represent data - Exposes data in SPARQL endpoint/RDF dump - Knows SPARQL queries Web developer - Unfamiliar with ontologies/vocabularies used - Uses JSON to read and manipulate data - Uses REST APIs to retrieve data

5. Information Sciences Institute OBA: Ontology Based APIs OWL Ontology SPARQL endpoint OpenAPI Specification (OAS) REST API Server

6. Information Sciences Institute OBA: Ontology Based APIs OWL Ontology SPARQL endpoint OpenAPI Specification (OAS) REST API Server OWL to OAS Mapping Generate and test server Automated JSON to RDF handling Generate clients

8. Information Sciences Institute Mapping OWL to OAS OpenAPI specification (https://swagger.io/specification/) • Each class maps to an OAS “schema” – Mapping covers classes, subclasses, properties, data properties, domain, ranges, and some OWL constraints* – You can filter undesired paths • Each class has two path for GET: – /{ClassName} – /{ClassName}/{instanceID} • One path for PUT, POST and DELETE: – /{ClassName} [POST] – /{ClassName}/{instanceID} [PUT, DELETE] *More information: https://oba.readthedocs.io/en/latest/mapping/

9. Information Sciences Institute Mapping OWL to OAS: Example Person Student Student Record subclassOf hasRecord :Person rdf:type owl:Class ; rdfs:label "Person"@en. :Student rdf:type owl:Class ; rdfs:subClassOf :Person ; rdfs:label "Student"@en . :hasRecord rdf:type owl:ObjectProperty , owl:FunctionalProperty ; rdfs:domain :Student ; rdfs:range :StudentRecord ; rdfs:label "has record"@en . components: schemas: Person: type: object properties: name: type: string Student: allOf: - $ref: '#/components/schemas/Person' - type: object properties: hasRecord: items: $ref: '#/components/schemas/StudentRecord type: array maxItems: 1 OWL (ttl) OAS (yaml)

11. Information Sciences Institute Generating the server: Workflow OpenAPITools / openapi-generator stain / owl2jsonld

13. Information Sciences Institute From RDF to JSON https://w3c.github.io/json-ld-framing/

14. Information Sciences Institute Custom Queries Additional queries may be required in the API 1. Create a new query – CONSTRUCT 1. Define query parameters – Basil’s convention 1. Add path to OAS Basil custom_paths: /custom/models/variable: get: description: Get models by variable name parameters: - description: Name of the custom query in: query name: custom_query_name required: false schema: default: custom_models_variable type: string - description: variable to search in: query name: label required: true schema: type: string responses: 200: content: application/json: ...

16. Information Sciences Institute Generating your own client Example: https://model-catalog-python-api-client.readthedocs.io/en/latest/models/ ...

17. Information Sciences Institute Performance 150 ms (max) of delay 60 req/sec (With reverse proxy caching enabled)

18. Information Sciences Institute Conclusions and Future Work Using SPARQL endpoints as a non Semantic Web expert is challenging - Need to know SPARQL - Need to understand the ontologies used to represent the data - Need to understand documentation and examples OBA enables KG engineers to easily expose REST APIs from their ontologies/vocabularies: - Create an OAS specification from an ontology - Generate a REST server that accepts and returns JSON following the OAS - Generate tests Next for OBA: JSON-LD, GraphQL support, advanced SHACL validation

19. Information Sciences Institute Help us improve OBA Documentation: https://oba.readthedocs.io/en/latest/ GitHub: https://github.com/KnowledgeCaptureAndDiscovery/OBA/ Examples: https://oba.readthedocs.io/en/latest/examples/ OWL SPARQL JSON-LD OpenAPI + documentation REST JSON

20. Information Sciences Institute Acknowledgements Yolanda Gil Hernan Vargas Oscar Corcho Paola Espinoza Carlos Badenes Karl Hammar Anonymous ISWC reviewers This work was funded by the Defense Advanced Research Projects Agency with award W911NF-18-1-0027 and the National Science Foundation with award ICER-144032

21. Information Sciences Institute OBA: An Ontology-Based Framework for Creating REST APIs for Knowledge Graphs Daniel Garijo and Maximiliano Osorio dgarijo@isi.edu @dgarijov

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