File: README — Documentation for rdfobjects (0.11.4)

RDFObjects are intended to simplify working with RDF data by providing a (more) Ruby-like interface to resources (thanks to OpenStruct).

There is a Google Group at groups.google.com/group/rdfobjects to discuss problems, enhancements, changes, announcements, etc.

Installation:

The gem is currently hosted at http://gemcutter.org/gems/rdfobjects so you'll either need the gemcutter gem (and run "gem tumble") or add gemcutter.org to your sources manually (gem sources -a http://gemcutter.org).

$ sudo gem install rdfobjects

Requirements:

* Nokogiri (the idea is for more options in the future)
* curies
* json (or json_pure)

Usage:

>> require 'rdf_objects'

>> include RDFObject

>> Curie.add_prefixes! :skos=>"http://www.w3.org/2004/02/skos/core#"

>> resource = Resource.new('http://id.loc.gov/authorities/sh2002000569#concept')
>> resource.describe
>> resource.skos

=> {"inScheme"=>[#<RDFObject::Resource uri="http://id.loc.gov/authorities#topicalTerms">, #<RDFObject::Resource uri="http://id.loc.gov/authorities#conceptScheme">], "broader"=>[#<RDFObject::Resource skos={"prefLabel"=>"Semantic networks (Information theory)"}, uri="http://id.loc.gov/authorities/sh92004914#concept">, #<RDFObject::Resource skos={"prefLabel"=>"World Wide Web"}, uri="http://id.loc.gov/authorities/sh95000541#concept">, #<RDFObject::Resource skos={"prefLabel"=>"Semantic integration (Computer systems)"}, uri="http://id.loc.gov/authorities/sh2004000479#concept">], "closeMatch"=>#<RDFObject::Resource uri="http://stitch.cs.vu.nl/vocabularies/rameau/ark:/12148/cb14521343b">, "prefLabel"=>"Semantic Web"}

>> resource["[skos:prefLabel]"]

=> "Semantic Web"

>> resource.skos["prefLabel"]

=> "Semantic Web"

>> resource["http://www.w3.org/2004/02/skos/core#prefLabel"]

=> "Semantic Web"
(etc.)

>> resource.skos["broader"].first.skos["prefLabel"]

=> "Semantic networks (Information theory)"

Unnecessary, but helpful, way to define typed literals
>> source = Literal.new("Library of Congress Authorities", {:language=>"en"})

And assert them

>> resource.assert("http://purl.org/dc/terms/source", source)

=> ["Work cat.: 2002070545: The Semantic Web--ISWC 20002, 2002.", "ASTI on FirstSearch, May 6, 2002: in titles (semantic Web)", "Engr. index online, May 6, 2002 (identifier: Semantic Web)", "Library of Congress Authorities"]

>> resource["http://purl.org/dc/terms/source"].last.language

=> "en"

To relate a resource to another URI you can use #.relate - it will accept full uri strings, safe curies or other RDFObject::Resource objects

>> resource.relate("[skos:closeMatch]", "http://dbpedia.org/resource/Category:Semantic_Web")

=> [#<RDFObject::Resource uri="http://stitch.cs.vu.nl/vocabularies/rameau/ark:/12148/cb14521343b">, #<RDFObject::Resource uri="http://dbpedia.org/resource/Category:Semantic_Web">]

These relationships are actually replaced with RDFObject::ResourceReference objects (to prevent massive recursion errors).  To access the actual Resource object, use:

>> resource["[skos:closeMatch]"].first.resource

=> #<RDFObject::Resource uri="http://stitch.cs.vu.nl/vocabularies/rameau/ark:/12148/cb14521343b">

In order to be sure you are always asserting against the same object, use RDFObject::Collection objects to manage your Resources.

>> collection = Collection.new

=> {}

>> r1 = collection.find_or_create('http://ex.org/ex/1234')

=> #<RDFObject::Resource uri="http://ex.org/ex/1234">

>> r1.object_id

=> 8996290

>> r2 = collection.find_or_create('http://ex.org/ex/1234')

=> #<RDFObject::Resource uri="http://ex.org/ex/1234">  

>> r2.object_id

=> 8996290  

So relationships and assertions are always applied to the same objects.

You can delete a single resource:

>> collection.remove(r1)

>> collection
=> {}

There is also a convenience method on RDFObject::Collection to help find particular resources by predicate:

>> resources_with_types = collection.find_by_predicate("http://www.w3.org/1999/02/22-rdf-syntax-ns#type")

And to find resources by predicate and object:

>> resources_i_want = collection.find_by_predicate_and_object("http://www.w3.org/2004/02/skos/core#closeMatch", "http://stitch.cs.vu.nl/vocabularies/rameau/ark:/12148/cb145537755")

Both these return RDFObject::Collection objects with your matches.  Changes to resources in these collections also affect the resource in original collection.

There are also parsers for ntriples, rdf/xml, RSS 1.0, RDFa, and JSON.  Parsers return a RDFObject::Collection with all of the resources discovered in the RDF source.

>> resources = Parser.parse(open('lcsh.nt').read)

>> resources.values.first

=> #<RDFObject::Resource n0={"altLabel"=>"Lichen ruber planus", "inScheme"=>[#<RDFObject::Resource uri="http://id.loc.gov/authorities#conceptScheme">, #<RDFObject::Resource uri="http://id.loc.gov/authorities#topicalTerms">], "prefLabel"=>"Lichen planus"}, n1={"sameAs"=>#<RDFObject::Resource uri="info:lc/authorities/sh85076767">}, uri="http://id.loc.gov/authorities/sh85076767#concept", n2={"modified"=>#<DateTime: 211644344801/86400,-1/6,2299161>}, rdf={"type"=>#<RDFObject::Resource uri="http://www.w3.org/2004/02/skos/core#Concept">}>

There are serializers for RDF/XML and ntriples.  Both resources and collections can be serialized.

>> resource.to_xml

=> "<rdf:RDF xmlns:n0="http://www.w3.org/2004/02/skos/core#" xmlns:n1="http://www.w3.org/2002/07/owl#" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:n2="http://purl.org/dc/terms/"><rdf:Description rdf:about="http://id.loc.gov/authorities/sh85076767#concept"><n0:altLabel>Lichen ruber planus</n0:altLabel><n0:inScheme><rdf:Description rdf:about="http://id.loc.gov/authorities#conceptScheme"></rdf:Description></n0:inScheme><n0:inScheme><rdf:Description rdf:about="http://id.loc.gov/authorities#topicalTerms"></rdf:Description></n0:inScheme><n0:prefLabel>Lichen planus</n0:prefLabel><n1:sameAs><rdf:Description rdf:about="info:lc/authorities/sh85076767"></rdf:Description></n1:sameAs><n2:modified rdf:datatype="http://www.w3.org/2001/XMLSchema#dateTime">1994-08-22T15:46:41-04:00</n2:modified><rdf:type><rdf:Description rdf:about="http://www.w3.org/2004/02/skos/core#Concept"></rdf:Description></rdf:type></rdf:Description></rdf:RDF>"

>> collection.to_xml

>> resource.to_ntriples

=> "<http://id.loc.gov/authorities/sh85076767#concept> <http://www.w3.org/2004/02/skos/core#altLabel> "Lichen ruber planus"@en.\n<http://id.loc.gov/authorities/sh85076767#concept> <http://www.w3.org/2004/02/skos/core#inScheme> <http://id.loc.gov/authorities#conceptScheme>.\n<http://id.loc.gov/authorities/sh85076767#concept> <http://www.w3.org/2004/02/skos/core#inScheme> <http://id.loc.gov/authorities#topicalTerms>.\n<http://id.loc.gov/authorities/sh85076767#concept> <http://www.w3.org/2004/02/skos/core#prefLabel> "Lichen planus"@en.\n<http://id.loc.gov/authorities/sh85076767#concept> <http://www.w3.org/2002/07/owl#sameAs> <info:lc/authorities/sh85076767>.\n<http://id.loc.gov/authorities/sh85076767#concept> <http://purl.org/dc/terms/modified> "1994-08-22T15:46:41-04:00"^^<http://www.w3.org/2001/XMLSchema#dateTime>.\n<http://id.loc.gov/authorities/sh85076767#concept> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.w3.org/2004/02/skos/core#Concept>.\n"

>> collection.to_ntriples

etc.