Abstract

N-Quads is a line-based, plain text format for encoding an RDF dataset.

Status of This Document

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.

The N-Quads format has a similar flavor as N-Triples [N-TRIPLES]. The main distinction is that N-Quads allows encoding multiple graphs. In a change from previous publication, this document is intended to become a W3C Recommendation.

This document was published by the RDF Working Group as a Proposed Recommendation. This document is intended to become a W3C Recommendation. The W3C Membership and other interested parties are invited to review the document and send comments to public-rdf-comments@w3.org (subscribe, archives) through 04 February 2013. Advisory Committee Representatives should consult their WBS questionnaires. Note that substantive technical comments were expected during the Last Call review period that ended 14 October 2013.

Please see the Working Group's implementation report.

Publication as a Proposed Recommendation does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

Table of Contents

1. Introduction

This document defines N-Quads, an easy to parse, line-based, concrete syntax for RDF Datasets [RDF11-CONCEPTS].

N-quads statements are a sequence of RDF terms representing the subject, predicate, object and graph label of an RDF Triple and the graph it is part of in a dataset. These may be separated by white space (spaces #x20 or tabs #x9). This sequence is terminated by a '.' and a new line (optional at the end of a document).

Example 1

2. N-Quads Language

2.1 Simple Statements

The simplest statement is a sequence of (subject, predicate, object) terms forming an RDF triple and an optional blank node label or IRI labeling what graph in a dataset the triple belongs to, all are separated by whitespace and terminated by '.' after each statement.

Example 2

The graph label IRI can be omitted, in which case the triples are considered part of the default graph of the RDF dataset.

2.2 IRIs

IRIs may be written only as absolute IRIs. IRIs are enclosed in '<' and '>' and may contain numeric escape sequences (described below). For example <http://example.org/#green-goblin>.

2.3 RDF Literals

Literals are used to identify values such as strings, numbers, dates.

Literals (Grammar production Literal) have a lexical form followed by a language tag, a datatype IRI, or neither. The representation of the lexical form consists of an initial delimiter " (U+0022), a sequence of permitted characters or numeric escape sequence or string escape sequence, and a final delimiter. Literals may not contain the characters ", LF, or CR. In addition '\' (U+005C) may not appear in any quoted literal except as part of an escape sequence. The corresponding RDF lexical form is the characters between the delimiters, after processing any escape sequences. If present, the language tag is preceded by a '@' (U+0040). If there is no language tag, there may be a datatype IRI, preceeded by '^^' (U+005E U+005E). If there is no datatype IRI and no language tag, the datatype is xsd:string.

2.4 RDF Blank Nodes

RDF blank nodes in N-Quads are expressed as _: followed by a blank node label which is a series of name characters. The characters in the label are built upon PN_CHARS_BASE, liberalized as follows:

A fresh RDF blank node is allocated for each unique blank node label in a document. Repeated use of the same blank node label identifies the same RDF blank node.

Example 3

3. Conformance

As well as sections marked as non-normative, all authoring guidelines, diagrams, examples, and notes in this specification are non-normative. Everything else in this specification is normative.

The key words MUST, MUST NOT, REQUIRED, SHOULD, SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL in this specification are to be interpreted as described in [RFC2119].

This specification defines conformance criteria for:

A conforming N-Quads document is a Unicode string that conforms to the grammar and additional constraints defined in section 4. Grammar, starting with the nquadsDoc production. An N-Quad document serializes an RDF dataset.

Note

N-Quads documents do not provide a way of serializing empty graphs that may be part of an RDF dataset.

A conforming N-Quads parser is a system capable of reading N-Quads documents on behalf of an application. It makes the serialized RDF graph, as defined in section 5. Parsing, available to the application, usually through some form of API.

The IRI that identifies the N-Quads language is: http://www.w3.org/ns/formats/N-Quads

3.1 Media Type and Content Encoding

The media type of N-Quads is application/n-quads. The content encoding of N-Quads is always UTF-8. See N-Quads Media Type for the media type registration form.

3.1.1 Other Media Types

The original specification, N-Quads: Extending N-Triples with Context, proposed the use of media type text/x-nquads with an encoding using 7-bit US-ASCII.

4. Grammar

An N-Quads document is a Unicode[UNICODE] character string encoded in UTF-8. Unicode code points only in the range U+0 to U+10FFFF inclusive are allowed.

White space (tab U+0009 or space U+0020) is used to separate two terminals which would otherwise be (mis-)recognized as one terminal. White space is significant in the production STRING_LITERAL_QUOTE.

Comments in N-Quads take the form of '#', outside an IRIREF or STRING_LITERAL_QUOTE, and continue to the end of line (EOL) or end of file if there is no end of line after the comment marker. Comments are treated as white space.

The EBNF used here is defined in XML 1.0 [EBNF-NOTATION].

Escape sequence rules are the same as Turtle [TURTLE]. However, as only the STRING_LITERAL_QUOTE production is allowed new lines in literals MUST be escaped.

[1] nquadsDoc ::= statement? (EOL statement)* EOL?
[2] statement ::= subject predicate object graphLabel? '.'
[3] subject ::= IRIREF | BLANK_NODE_LABEL
[4] predicate ::= IRIREF
[5] object ::= IRIREF | BLANK_NODE_LABEL | literal
[6] graphLabel ::= IRIREF | BLANK_NODE_LABEL
[7] literal ::= STRING_LITERAL_QUOTE ('^^' IRIREF | '@' LANGTAG)?

Productions for terminals

[144s] LANGTAG ::= '@' [a-zA-Z]+ ('-' [a-zA-Z0-9]+)*
[8] EOL ::= [#xD#xA]+
[10] IRIREF ::= '<' ([^#x00-#x20<>"{}|^`\] | UCHAR)* '>'
[11] STRING_LITERAL_QUOTE ::= '"' ([^#x22#x5C#xA#xD] | ECHAR | UCHAR)* '"'
[141s] BLANK_NODE_LABEL ::= '_:' (PN_CHARS_U | [0-9]) ((PN_CHARS | '.')* PN_CHARS)?
[12] UCHAR ::= '\u' HEX HEX HEX HEX | '\U' HEX HEX HEX HEX HEX HEX HEX HEX
[153s] ECHAR ::= '\' [tbnrf"'\]
[157s] PN_CHARS_BASE ::= [A-Z] | [a-z] | [#x00C0-#x00D6] | [#x00D8-#x00F6] | [#x00F8-#x02FF] | [#x0370-#x037D] | [#x037F-#x1FFF] | [#x200C-#x200D] | [#x2070-#x218F] | [#x2C00-#x2FEF] | [#x3001-#xD7FF] | [#xF900-#xFDCF] | [#xFDF0-#xFFFD] | [#x10000-#xEFFFF]
[158s] PN_CHARS_U ::= PN_CHARS_BASE | '_' | ':'
[160s] PN_CHARS ::= PN_CHARS_U | '-' | [0-9] | #x00B7 | [#x0300-#x036F] | [#x203F-#x2040]
[162s] HEX ::= [0-9] | [A-F] | [a-f]

5. Parsing

Parsing N-Quads requires a state of one item:

5.1 RDF Term Constructors

This table maps productions and lexical tokens to RDF terms or components of RDF terms listed in section 5. Parsing:

productiontypeprocedure
IRIREF IRI The characters between "<" and ">" are taken, with the escape sequences unescaped, to form the unicode string of the IRI.
STRING_LITERAL_QUOTE lexical formThe characters between the outermost '"'s are taken, with escape sequences unescaped, to form the unicode string of a lexical form.
LANGTAG language tagThe characters following the @ form the unicode string of the language tag.
literal literal The literal has a lexical form of the first rule argument, STRING_LITERAL_QUOTE, and either a language tag of LANGTAG or a datatype IRI of iri, depending on which rule matched the input. if neither a language tag nor a datatype IRI is provided, the literal has a datatype of xsd:string.
BLANK_NODE_LABEL blank node The string matching the second argument, PN_LOCAL, is a key in bnodeLabels. If there is no corresponding blank node in the map, one is allocated.

5.2 RDF Dataset Construction

An N-Quads document defines an RDF dataset composed of RDF graphs composed of a set of RDF triples. The statement production produces a triple defined by the terms constructed for subject, predicate and object. This RDF triple is added to the graph labeled by the production graphLabel, if no graphLabel is present the triple is added to the RDF datasets default graph.

6. Acknowledgements

This section is non-normative.

The editor of the RDF 1.1 edition acknowledges valuable contributions from Gregg Kellogg, Andy Seaborne, Eric Prud'hommeaux, Dave Beckett, David Robillard, Gregory Williams, Antoine Zimmermann, Sandro Hawke, Richard Cyganiak, Pat Hayes, Henry S. Thompson, Bob Ferris, Henry Story, Andreas Harth, Lee Feigenbaum, Peter Ansell, and David Booth.

This specification is a product of extended deliberations by the members of the RDF Working Group chaired by Guus Schreiber and David Wood. It draws upon the eariler specification in N-Quads: Extending N-Triples with Context, edited by Richard Cyganiak, Andreas Harth, and Aidan Hogan.

A. Change Log

A.1 Changes between Candidate Recommendation 05 November 2013 and this Proposed Recommendation

A.2 Changes between Last Call Working Draft 05 September 2013 and Candidate Recommendation 05 November 2013

No substitutive changes.

A.3 Changes since original publication as Note

B. N-Quads Internet Media Type, File Extension and Macintosh File Type

Contact:
Eric Prud'hommeaux
See also:
How to Register a Media Type for a W3C Specification
Internet Media Type registration, consistency of use
TAG Finding 3 June 2002 (Revised 4 September 2002)

The Internet Media Type / MIME Type for N-Quads is "application/n-quads".

It is recommended that N-Quads files have the extension ".nq" (all lowercase) on all platforms.

It is recommended that N-Quads files stored on Macintosh HFS file systems be given a file type of "TEXT".

This information that follows will be submitted to the IESG for review, approval, and registration with IANA.

Type name:
application
Subtype name:
n-quads
Required parameters:
None
Optional parameters:
None
Encoding considerations:
The syntax of N-Quads is expressed over code points in Unicode [UNICODE]. The encoding is always UTF-8 [UTF-8].
Unicode code points may also be expressed using an \uXXXX (U+0 to U+FFFF) or \UXXXXXXXX syntax (for U+10000 onwards) where X is a hexadecimal digit [0-9A-F]
Security considerations:
N-Quads is a general-purpose assertion language; applications may evaluate given data to infer more assertions or to dereference IRIs, invoking the security considerations of the scheme for that IRI. Note in particular, the privacy issues in [RFC3023] section 10 for HTTP IRIs. Data obtained from an inaccurate or malicious data source may lead to inaccurate or misleading conclusions, as well as the dereferencing of unintended IRIs. Care must be taken to align the trust in consulted resources with the sensitivity of the intended use of the data; inferences of potential medical treatments would likely require different trust than inferences for trip planning.
N-Quads is used to express arbitrary application data; security considerations will vary by domain of use. Security tools and protocols applicable to text (e.g. PGP encryption, MD5 sum validation, password-protected compression) may also be used on N-Quads documents. Security/privacy protocols must be imposed which reflect the sensitivity of the embedded information.
N-Quads can express data which is presented to the user, for example, RDF Schema labels. Application rendering strings retrieved from untrusted N-Quads documents must ensure that malignant strings may not be used to mislead the reader. The security considerations in the media type registration for XML ([RFC3023] section 10) provide additional guidance around the expression of arbitrary data and markup.
N-Quads uses IRIs as term identifiers. Applications interpreting data expressed in N-Quads should address the security issues of Internationalized Resource Identifiers (IRIs) [RFC3987] Section 8, as well as Uniform Resource Identifier (URI): Generic Syntax [RFC3986] Section 7.
Multiple IRIs may have the same appearance. Characters in different scripts may look similar (a Cyrillic "о" may appear similar to a Latin "o"). A character followed by combining characters may have the same visual representation as another character (LATIN SMALL LETTER E followed by COMBINING ACUTE ACCENT has the same visual representation as LATIN SMALL LETTER E WITH ACUTE). Any person or application that is writing or interpreting data in Turtle must take care to use the IRI that matches the intended semantics, and avoid IRIs that make look similar. Further information about matching of similar characters can be found in Unicode Security Considerations [UNICODE-SECURITY] and Internationalized Resource Identifiers (IRIs) [RFC3987] Section 8.
Interoperability considerations:
There are no known interoperability issues.
Published specification:
This specification.
Applications which use this media type:
No widely deployed applications are known to use this media type. It may be used by some web services and clients consuming their data.
Additional information:
Magic number(s):
None.
File extension(s):
".nq"
Macintosh file type code(s):
"TEXT"
Person & email address to contact for further information:
Eric Prud'hommeaux <eric@w3.org>
Intended usage:
COMMON
Restrictions on usage:
None
Author/Change controller:
The N-Quads specification is the product of the RDF WG. The W3C reserves change control over this specifications.

C. References

C.1 Normative references

[EBNF-NOTATION]
Tim Bray; Jean Paoli; C. M. Sperberg-McQueen; Eve Maler; François Yergeau. EBNF Notation 26 November 2008. W3C Recommendation. URL: http://www.w3.org/TR/REC-xml/#sec-notation
[RDF11-CONCEPTS]
Richard Cyganiak, David Wood, Markus Lanthaler, Editors. RDF 1.1 Concepts and Abstract Syntax. 5 November 2013. W3C Candidate Recommendation (work in progress). URL: http://www.w3.org/TR/2013/CR-rdf11-concepts-20131105/. The latest edition is available at http://www.w3.org/TR/rdf11-concepts/
[RFC2119]
S. Bradner. Key words for use in RFCs to Indicate Requirement Levels. March 1997. Internet RFC 2119. URL: http://www.ietf.org/rfc/rfc2119.txt
[RFC3023]
M. Murata; S. St.Laurent; D. Kohn. XML Media Types (RFC 3023). January 2001. RFC. URL: http://www.ietf.org/rfc/rfc3023.txt
[RFC3986]
T. Berners-Lee; R. Fielding; L. Masinter. Uniform Resource Identifier (URI): Generic Syntax (RFC 3986). January 2005. RFC. URL: http://www.ietf.org/rfc/rfc3986.txt
[RFC3987]
M. Dürst; M. Suignard. Internationalized Resource Identifiers (IRIs). January 2005. RFC. URL: http://www.ietf.org/rfc/rfc3987.txt
[UNICODE]
The Unicode Standard. URL: http://www.unicode.org/versions/latest/
[UTF-8]
F. Yergeau. UTF-8, a transformation format of ISO 10646. IETF RFC 3629. November 2003. URL: http://www.ietf.org/rfc/rfc3629.txt

C.2 Informative references

[N-TRIPLES]
Gavin Carothers, Andy Seabourne. RDF 1.1 N-Triples. 5 November 2013. W3C Candidate Recommendation (work in progress). URL: http://www.w3.org/TR/2013/CR-n-triples-20131105/. The latest edition is available at http://www.w3.org/TR/n-triples/
[TURTLE]
Eric Prud'hommeaux, Gavin Carothers, Editors. RDF 1.1 Turtle: Terse RDF Triple Language. 19 February 2013. W3C Candidate Recommendation (work in progress). URL: http://www.w3.org/TR/2013/CR-turtle-20130219/. The latest edition is available at http://www.w3.org/TR/turtle/
[UNICODE-SECURITY]
Mark Davis; Michel Suignard. Unicode Security Considerations. URL: http://www.unicode.org/reports/tr36/