1) GRLC is a tool that generates Linked Data APIs from SPARQL queries stored in a GitHub repository. It automatically builds Swagger specifications and API code by mapping the GitHub repository structure and SPARQL queries. 2) This allows SPARQL queries to be organized and maintained externally to applications in a version controlled way. The APIs generated hide the complexity of SPARQL from clients. 3) GRLC was used to build APIs for accessing historical census data, hiding SPARQL from historians. It was also used to reduce coupling between SPARQL and R code for a project analyzing the impact of early life conditions on later outcomes.

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GRLC MAKES GITHUB TASTE
LIKE LINKED DATA APIS
Chefs
Albert Meroño-Peñuela
Rinke Hoekstra
Services and Applications over
Linked APIs and Data (SALAD)
ESWC
29-05-2016

2. Vrije Universiteit Amsterdam
 VU University Amsterdam – Computer
Science (Knowledge Representation &
Reasoning group)
 International Institute of Social
History (IISG), Amsterdam
 CLARIAH – National Infrastructure for
Digital Humanities
> DataLegend : Structured Data Hub
 Previously incubated by CEDAR –
Dutch historical censuses as 5-star
LOD
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INSTITUTIONAL SLIDE

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DISCLAIMER
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Frustration-
driven
research

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1. LD-CONSUMING
APPLICATIONS
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5 Het begint met een idee
 Publishing Dutch historical
censuses as 5-star LD
> Intensive use of RDF Data Cube
> Harmonization rules
> Provenance
 1st historical census data as Linked
Data (1795-1971)
 8 million observations (sex, marital
status, occupation position, housing type,
residence status)
 External links
> Geographical: 2.7M
> Occupations: 350K
> Belief: 250K
 High value for social historians
5 Faculty / department / title presentation
THE CEDAR STORY

6. Vrije Universiteit Amsterdam
 Historians can’t really write SPARQL
 Variety of access interfaces needed
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CENSUS DATA QUERYING INTERFACES

7. Vrije Universiteit Amsterdam
 CLARIAH-WP4: Structured
data hub for social historians
 IPUMS, NAPP, CEDAR, etc
> Macro-, micro-, meso-data
> Civil registries, occupation, religion,
country-level economic indicators
> National (Netherlands) and
international
 Mostly CSV tables turned
into RDF Data Cube and
CSVW
 More than 1B triples already
 Higher variety of humanities
scholars  higher variety of
data access requirements)
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SCALING VARIETY
Exi sts
Frequency Table
Variable does not yet existVariables
Mappings
Publish
Augment
Includes both external LinkedDataand
standard vocabularies, e.g. World Bank
External (Meta)Data
Existing Variables
& Codes
Provenance tracking of a
External Datasets
StructuredDataHub

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FRUSTRATION 1
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This is
SPARQL
mess!!!1one

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 One .rq file for SPARQL query
 Good support of query curation
processes
> Versioning
> Branching
> Clone-pull-push
 Web-friendly features!
> One URI per query
> Uniquely identifiable
> De-referenceable
(raw.githubusercontent.com)
11 Faculty / department / title presentation
GITHUB AS A HUB OF
SPARQL QUERIES

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LESSON 1
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Query
centralization
helps
maintaining
distributed
applications

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2. THE NEED FOR APIS
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14. Vrije Universiteit Amsterdam
 Linked Data APIs emerge
 RESTful entry point to Linked Data hubs for Web applications
 OpenPHACTS
 …but the Linked Data API (e.g. Swagger spec, code itself) still
needs to be coded and maintained
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MEANWHILE IN THE SEMANTIC WEB…

15. Vrije Universiteit Amsterdam
 Love story – thanks KMi!
 Automatically builds Swagger
specs and API code
 Takes SPARQL queries as input
(1 API operation = 1 SPARQL
query)
> API call functionality limited to SPARQL
expressivity
 Makes SPARQL queries uniquely
referenceable by using their
equivalent LDA operation
> Stores SPARQL internally
> But we already have uniquely
referenceable SPARQL…
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BASIL

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FRUSTRATION 2
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Copy-pasting 200
queries!!!
&
Organization
problem

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 Cousin of BASIL in a SALAD 
 Same basic principle: 1 SPARQL
query = 1 API operation
 Automatically builds Swagger spec
and UI from SPARQL
But:
 External query management
 Organization of SPARQL queries in
the GitHub repo matches
organization of the API
 Thin layer – nothing stored server-
side
 Maps
> GitHub API
> Swagger spec
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18. Vrije Universiteit Amsterdam
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MAPPING GITHUB AND SWAGGER

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SPARQL DECORATOR SYNTAX

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THE GRLC SERVICE
 Assuming your repo is at https://github.com/:owner/:repo
and your grlc instance at :host,
> http://:host/:owner/:repo/spec returns the JSON swagger spec
> http://:host/:owner/:repo/api-docs returns the swagger UI
> http://:host/:owner/:repo/:operation?p_1=v_1...p_n=v_n calls
operation with specifiec parameter values
> Uses BASIL’s SPARQL variable name convention for query parameters
 Sends requests to
> https://api.github.com/repos/:owner/:repo to look for SPARQL queries and their
decorators
> https://raw.githubusercontent.com/:owner/:repo/master/file.rq to dereference
queries, get the SPARQL, and parse it

21. Vrije Universiteit Amsterdam
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SPICED-UP SWAGGER UI

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EVALUATION – USE CASES
 CEDAR: Access to census data for
historians
> Hides SPARQL
> Allows them to fill query parameters
through forms
> Co-existence of SPARQL and non-SPARQL
clients
 CLARIAH - Born Under a Bad Sign:
Do prenatal and early-life
conditions have an impact on
socioeconomic and health
outcomes later in life? (uses 1891
Canada and Sweden Linked Census Data)
> Reduction of coupling between SPARQL
libs and R
> Shorter R code – input stream as CSV

23. Vrije Universiteit Amsterdam
The spectrum of Linked Data clients: SPARQL intensive applications
vs RESTful API applications
grlc uses decoupling of SPARQL from all client applications
(including LDA) as a powerful practice
 Separates query curation workflows from everything else
 Allows at the same time
> Web-friendly SPARQL queries
> Web-friendly RESTful APIs
 Helps you to easily organise your LDA – just organise your SPARQL
repository and you’re set
 Try it out!
> http://grlc.clariah-sdh.eculture.labs.vu.nl
> https://github.com/CLARIAH/grlc
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CONCLUSIONS

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THANK YOU!
@ALBERTMERONYO
DATALEGEND.NET
CLARIAH.NL
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