rdf-prolog-interchange

Standalone RDF 1.2 <-> ISO Prolog interchange toolkit. It reversibly converts RDF dataset quads to ordinary rdf/4 Prolog facts and ground rdf/4 facts back to RDF. The package contains no Prolog solver.

RDF supplies the data model; ISO Prolog supplies the programming language. This package connects them with two converters and a small term mapping:

1. Convert RDF to rdf/4 facts.
2. Run your rules in a Prolog engine, if needed.
3. Write the results as ground rdf/4 facts and convert them back to RDF.

The mapping guide explains the representation and its practical limits. Why RDF and Prolog? explains the choice of tools. prolog-to-rdf reads facts without executing rules or directives. The converter preserves quads, but cannot preserve empty named graphs, which have no quads to encode.

Its vendored source parser is synchronized with EyeProlog’s parser while using a minimal standalone term model. See EXTRACTION.md for the source revision and the intentionally small adaptation boundary.

Install

npm install

Node.js 18+ is required. N-Quads/N-Triples use the built-in parser. rdf-parse is an optional dependency for Turtle, TriG, JSON-LD, RDF/XML, RDFa, and other RDF syntaxes.

Basic roundtrip

rdf-to-prolog data.ttl -o data.pl
prolog-to-rdf data.pl -o roundtripped.ttl

The Prolog representation is:

rdf(Subject, Predicate, Object, Graph).

prolog-to-rdf infers its output syntax from .nq, .ttl, or .trig (or use --format nq|ttl|trig).

Examples

examples/ contains 14 flat, complete examples. Every example has exactly the same five-file shape:

examples/<name>-input.ttl|trig
examples/<name>-input.pl
examples/<name>-rules.pl
examples/<name>-output.pl
examples/<name>-output.ttl|trig

The meaning is literal:

RDF input
   | rdf-to-prolog
   v
<name>-input.pl
   + <name>-rules.pl       (ISO Prolog)
   | query result_rdf/4
   v
<name>-output.pl           (ground rdf/4 test results)
   | prolog-to-rdf
   v
RDF output

All rule files expose:

result_rdf(S, P, O, G).
write_results.

result_rdf/4 is the query used by these examples. write_results/0 prints all its solutions as ground rdf/4 facts, the format accepted by prolog-to-rdf. Your program can use any query name; the converter only reads the resulting rdf/4 facts. See examples/README.md for a concrete trust-flow run.

With EyeProlog 1.5.26 or newer, materialize those facts without adding the resolved write_results goal to the output:

eyeprolog --quiet --goal write_results \
  examples/odrl-dpv-fpv-trust-flow-input.pl \
  examples/odrl-dpv-fpv-trust-flow-rules.pl \
  > examples/odrl-dpv-fpv-trust-flow-output.pl

CLI

RDF -> Prolog:

rdf-to-prolog [options] input

--format TYPE      input media type/extension when needed
--base IRI         base IRI for relative references
--rules FILE       append a rule file (optional convenience)
--include-source   store input as source_rdf/4 and bridge it through rdf/4
--scope NAME       blank-node scope
-o, --output FILE  output file

Prolog -> RDF:

prolog-to-rdf [options] facts.pl

--format nq|ttl|trig  RDF output syntax; otherwise inferred from -o
-o, --output FILE     output file

prolog-to-rdf does not execute rules. A Prolog engine first materializes the rule result as ground rdf/4 facts; the checked-in *-output.pl files show exactly what that means.

Aliases rdf-to-pl and pl-to-rdf are also provided.

JavaScript API

import {
  compileRdfDocumentToProlog,
  compileRdfToProlog,
  extractRdfFromProlog,
  serializeRdfFromProlog,
} from 'rdf-prolog-interchange';

const facts = compileRdfToProlog(nquads);
const nquadsAgain = extractRdfFromProlog(facts);
const turtle = serializeRdfFromProlog(facts, { format: 'ttl' });

Term mapping

RDF value	Prolog term
IRI	iri(Value)
Blank node	bnode(Scope, Label)
Typed literal	literal(Value, datatype(IRI))
Language string	literal(Value, lang(Language))
Directional language string	literal(Value, lang(Language, ltr)) / lang(Language, rtl)
RDF 1.2 triple term	triple(Subject, Predicate, Object)
Default graph	default_graph

RDF textual values are represented by ISO Prolog atoms. The publisher rejects Prolog strings and numbers in text positions instead of silently coercing them. IRIs must be absolute, language tags must follow RDF syntax, and RDF 1.2 base direction must be ltr or rtl.

Tests

npm test

The example test discovers all 14 names from the flat directory, verifies the five-file layout, roundtrips every checked-in input/output Prolog dataset, and verifies that every *-output.ttl|trig is exactly the prolog-to-rdf serialization of its matching *-output.pl. When rdf-parse is installed it also regenerates each *-input.pl from the original Turtle/TriG source.

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