SPARQL compiler functions for PostgreSQL

This is an extension for PostgreSQL.

It helps one query SPARQL datasources. SPARQL queries are compiled into Postgres views, so you can use them nicely in SQL.

It is currently used with Virtuoso, so it is useful with sources like dbpedia. It might or might not work with other RDF backends.

Installation

Install appropriate Perl packages

apt install libwww-perl libtry-tiny-perl

To build and install this module:

make
make install
make clean install installcheck

or selecting a specific PostgreSQL installation:

make PG_CONFIG=/some/where/bin/pg_config
make PG_CONFIG=/some/where/bin/pg_config install
make PG_CONFIG=/some/where/bin/pg_config installcheck
make PGPORT=5432 PG_CONFIG=/usr/lib/postgresql/10/bin/pg_config clean install installcheck

Make sure you set the connection parameters like PGPORT right for testing.

And finally inside the database:

CREATE EXTENSION sparql;

Using

Get data on a particular dbpedia resource:

SELECT * 
  FROM sparql.get_properties('dbpedia','http://dbpedia.org/resource/Johann_Sebastian_Bach');

SELECT * 
  FROM sparql.get_references('dbpedia','http://dbpedia.org/resource/Johann_Sebastian_Bach');

To compile a SPARQL query into SQL function + view:

SELECT sparql.compile_query(endpoint, identifier, sparql_query[, grouping]);

SPARQL endpoint is queried to determine the result format for the specified query. Then function identitier() and view identifier are created. Created function queries any SPARQL endpoint and returns result as SQL table. Created view is just a convenience layer over the created function. Once created, these can be further tweaked manualy for extra functionality.

Parameters:

• endpoint - default SPARQL endpoint.
• identifier - SQL identifier of function and view to be created, with or without schema
• sparql_query - SPARQL query to run
• grouping - optional array of identifiers to group by. Grouping is done in a view. When grouping, distinct values of non-grouped columns are aggregated into arrays.

for example:

SELECT sparql.compile_query('dbpedia','ludwig_van',$$
select ?predicate, ?object
where {
 <http://dbpedia.org/resource/Ludwig_van_Beethoven> ?predicate ?object.
}
$$,'{predicate}');

SELECT * from ludwig_van;