CL-NTRIPLES provides a simple parser for the N-Triples data format as defined by the W3C for storing RDF/Semantic information. N-Triples is a line-based, plain text format for encoding an RDF graph.

Main entry function is PARSE-NT method that parses N-Triples from the given source. This method accepts a file pathname, an input stream, or a string.

Returns a list of triples consisting of three elements: subject, predicate, object. Subjects can be either an uriref or a nodeID. Objects can be of three types: uriref, nodeID or a literal. Depending on the type of the object it is encoded into an association list.

N-Triples data format standard definition is provided in the W3C documents:

• RDF Testcases, N-Triples

Check also the Semantic Web page on CLiki.

Project page on Sourceforge.

Sample usage

CL-NTRIPLES is available through Quicklisp:

(ql:quickload :cl-ntriples)

CL-NTRIPLES was developed for a practical purpose of accessing the wealth of data accumulated by the DBPedia project. For example, let's query information about a Ukrainian city of Chernihiv (wiki, dbpedia):

(defvar page-url "http://dbpedia.org/data/Chernihiv.ntriples")
(defvar *res* (nt:parse-nt (drakma:http-request page-url)))
;; *res* now contains a list of triples, let's query some predicates
;; for brevity, predicates will defined as variables

(defconstant +prop-area-total-km+ "http://dbpedia.org/property/areaTotalKm")
(defconstant +rdf-label+ "http://www.w3.org/2000/01/rdf-schema#label")

;; querying predicates is now reduced to a simple function call:
;; nt:predicate? TRIPLES PREDICATE &key LANG DATA-TYPE

;; what is the city area in km2?
(nt:predicate? *res* +prop-area-total-km+)
=> (("http://dbpedia.org/resource/Chernihiv"
  "http://dbpedia.org/property/areaTotalKm"
  ((:LITERAL-STRING . "79")
   (:URIREF . "http://www.w3.org/2001/XMLSchema#int"))))

;; how do Japanese call this city?
(predicate? *res* +rdf-label+ :lang "ja")
=> (("http://dbpedia.org/resource/Chernihiv"
  "http://www.w3.org/2000/01/rdf-schema#label"
  (:LITERAL-STRING "チェルニーヒウ" :LANG "ja")))

Functions

Package provides following functions:

• PARSE-NT src
  Parses and returns a list of triples

• PREDICATE? triples predicate &key lang data-type
  filters out triples with matching predicates. Additional parameters (lang and data-type) can be used to limit returned triples to those with matching language and data type specifiers.

• LITERAL-STRING triple
  returns the literal-string value of the given triple.