rdf_fdw

Overview

Version

Build

You can build the RPM / DEB packages for rdf_fdw using pig build:

pig build pkg rdf_fdw         # build RPM / DEB packages

Install

You can install rdf_fdw directly. First, make sure the PGDG and PIGSTY repositories are added and enabled:

pig repo add pgsql -u          # Add repo and update cache

Install the extension using pig or apt/yum/dnf:

• Install
• pig
• dnf
• apt

pig install rdf_fdw;          # Install for current active PG version

pig ext install -y rdf_fdw -v 18  # PG 18
pig ext install -y rdf_fdw -v 17  # PG 17
pig ext install -y rdf_fdw -v 16  # PG 16
pig ext install -y rdf_fdw -v 15  # PG 15
pig ext install -y rdf_fdw -v 14  # PG 14

dnf install -y rdf_fdw_18       # PG 18
dnf install -y rdf_fdw_17       # PG 17
dnf install -y rdf_fdw_16       # PG 16
dnf install -y rdf_fdw_15       # PG 15
dnf install -y rdf_fdw_14       # PG 14

apt install -y postgresql-18-rdf-fdw   # PG 18
apt install -y postgresql-17-rdf-fdw   # PG 17
apt install -y postgresql-16-rdf-fdw   # PG 16
apt install -y postgresql-15-rdf-fdw   # PG 15
apt install -y postgresql-14-rdf-fdw   # PG 14

Create Extension:

CREATE EXTENSION rdf_fdw;

Usage

Sources: README, v2.4 release

rdf_fdw is a foreign data wrapper for RDF triplestores exposed through SPARQL endpoints. It lets PostgreSQL query RDF data with SQL, supports SQL clause pushdown, adds an rdfnode type for RDF terms, and includes SPARQL 1.1 function support.

Register a SPARQL Endpoint

Register a SPARQL endpoint with CREATE SERVER:

CREATE SERVER dbpedia
FOREIGN DATA WRAPPER rdf_fdw
OPTIONS (endpoint 'https://dbpedia.org/sparql');

The README documents server options such as:

• endpoint (required)
• batch_size
• enable_pushdown
• format
• http_proxy
• connect_timeout

In v2.4, proxy credentials were moved out of SERVER options and into USER MAPPING for security.

User Mapping and Foreign Tables

CREATE USER MAPPING FOR postgres
SERVER dbpedia
OPTIONS (user 'admin', password 'secret');

rdf_fdw works by declaring foreign tables that embed SPARQL queries and map result variables to PostgreSQL columns. The README also highlights native RDF node handling through the custom rdfnode type.

CREATE FOREIGN TABLE film (
  film_id text OPTIONS (variable '?film', nodetype 'iri'),
  name text OPTIONS (variable '?name', nodetype 'literal', literal_type 'xsd:string')
)
SERVER dbpedia
OPTIONS (sparql 'SELECT ?film ?name WHERE { ?film dbp:name ?name }');

Pushdown, DML, and Helpers

The upstream docs specifically call out pushdown for:

• WHERE
• LIMIT
• ORDER BY
• DISTINCT

They also document data modification support:

• INSERT
• UPDATE
• DELETE

Batching for SPARQL UPDATE traffic is controlled with the batch_size option.

The README lists utility functions including:

• rdf_fdw_version()
• rdf_fdw_settings()
• rdf_fdw_clone_table()

It also documents broader SPARQL function coverage, including aggregates, string functions, numeric functions, date/time functions, hash functions, and custom functions.

Caveats

The current README warns that retrieved RDF data is loaded into memory before conversion for PostgreSQL, so large result sets require adequate PostgreSQL memory. It also documents PostgreSQL 9.5+ as the supported baseline.