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N-Quads Format (RDF)

Description​

N-Quads is an extension of N-Triples that adds a fourth element (graph context) to each triple. It's used to represent RDF datasets with named graphs. Each line represents a single RDF quad (subject-predicate-object-graph).

File Extensions​

  • .nq - N-Quads files
  • .nquads - N-Quads files (alias)

Implementation Details​

Reading​

The N-Quads implementation:

  • Extends N-Triples implementation
  • Parses N-Quads format line by line
  • Extracts subject, predicate, object, and graph from each line
  • Converts each quad to a dictionary
  • Supports streaming for large files

Writing​

Writing support:

  • Writes one quad per line, including an optional graph field
  • Same subject/predicate/object keys as N-Triples

Key Features​

  • Line-based: One quad per line
  • Graph context: Includes graph identifier
  • RDF dataset: Represents RDF datasets with named graphs
  • Totals support: Can count total quads
  • Streaming: Processes files line by line

Usage​

from iterable import open_iterable

# Basic reading
with open_iterable('data.nq') as source:
    for row in source:
        print(row)  # Contains: subject, predicate, object, graph

# Writing
with open_iterable('output.nq', mode='w') as dest:
    dest.write({
        'subject': 'http://example.org/alice',
        'predicate': 'http://xmlns.com/foaf/0.1/name',
        'object': 'Alice',
        'graph': 'http://example.org/graph',
    })

Parameters​

  • encoding (str): File encoding (default: utf8)

N-Quads Format Structure​

Format: subject predicate object graph .

  • subject: URI or blank node
  • predicate: URI
  • object: URI, literal, or blank node
  • graph: Graph identifier (URI or blank node)
  • period: Ends each quad

Limitations​

  1. Line-based format: Each quad must fit on a single line
  2. No abbreviations: More verbose than Turtle
  3. Flat structure: Each quad is separate (no grouping)

Compression Support​

N-Quads files can be compressed with all supported codecs:

  • GZip (.nq.gz)
  • BZip2 (.nq.bz2)
  • LZMA (.nq.xz)
  • LZ4 (.nq.lz4)
  • ZIP (.nq.zip)
  • Brotli (.nq.br)
  • ZStandard (.nq.zst)

Use Cases​

  • RDF datasets: Working with RDF datasets with named graphs
  • Linked data: Processing linked data with graph context
  • Knowledge graphs: Building knowledge graphs with multiple graphs
  • Data exchange: RDF dataset exchange

Error Handling​

  • Missing dependency: optional libraries raise ImportError with an install hint (pip install 'iterabledata[<extra>]' when an extra exists).
  • Write mode: read-only formats raise WriteNotSupportedError or ValueError when opened with mode="w".
  • Bad or unsupported input: may raise ValueError, OSError, or library-specific errors.
  • See Troubleshooting for decoding, detection, and engine issues.
  • N-Triples - Simpler format without graph context
  • Turtle - More compact RDF format
  • RDF/XML - RDF in XML format