guide to publishing linked data on the Web. • In particular, how to construct good URIs for the things described by that data, and how to make sure that the data can be easily retrieved and processed. • These are not rules — they are guidelines to promote interoperability.
the data about that thing. * Attempting to retrieve a representation of the resource associated with that URI. For example, dereferencing an http: URI involves performing an HTTP request for it.
good idea to use http: or https: URIs to identify your things. • This brings about its own problem: what kind of URIs should refer to documents, and what to things described by those documents? Implications
the URIs for things described by documents; don’t use fragments for the URIs of the documents. • Fragment identifiers are never sent as part of HTTP requests (to do so is a direct violation of the protocol). • To a server, the “hash” and “hashless” URIs look the same, and so return the same document. • This is generally the simplest and most straightforward disambiguation mechanism. Use “hash” URIs
• A thing described by that document Dereferencing either URI will result in the same document — and which can contain distinct descriptions of both the document and thing (“This data was published yesterday” versus “this book was published a year ago”).
• A thing described by that document Others linking to your data and referring to the thing you describe can differentiate between them properly (“I like this data” versus “I like this animal”).
representations of documents to different clients. • RDF/XML is the most widely-supported serialisation of RDF in consumers at present. • The data format landscape doesn’t stand still: best practice will change over time. • Other RDF serialisations (and non-RDF formats) exist, and it’s good to serve them too if you can. Implications
responses. • Include a Content-‐Location header in your responses, giving the URL of the specific representation being served to the consumer. • Include a Alternates header in your responses to describe different variants.
HTML representations. • Use predictable extensions as part of your representation-specific URLs: e.g., .rdf, .json, .html — this doesn’t aid software, but does make developers’ lives easier. • If possible, include information about your documents and the various available representations in those documents.
HTML RDF/XML Includes an Accept header Content-Location: http://example.com/items/abc1234.html Content-Location: http://example.com/items/abc1234.rdf representations server picks a suitable representation based upon the Accept header
your canonical URIs. • Avoid deriving URIs from metadata liable to need correction or otherwise changing over time (such as titles). • When URIs do eventually need to change, handle this gracefully through 301 redirects and 410 (“Gone”) responses. Implications
permanent identifier. • Does not need to change even when corrections or other changes to the data are made. • Follows a pattern (/items/:id#thing), which aids developers’ understanding.
your “machine- facing” structured data in two completely different places. • Use predictable consistent patterns. • Publish dataset descriptions describing search endpoints, URI patterns, and providing examples. • Publish a “root” dataset on your domain root, or at /.well-‐known/void (or both). Implications
“owned” by other people: create your own identifiers for them and link between them. • Similarly, if you can, link to other people publishing descriptions of things you “own”. • Use owl:sameAs to indicate where two URIs really do refer to the same thing. • Don’t feel the need to generate your own URIs just for things you’re referencing, though — linking through other people’s URIs is fine (and good). Implications
Dodds and Ian Davis • http://www.w3.org/Provider/Style/URI.html • “Cool URIs don’t change” — Sir Tim Berners- Lee. • http://www.iana.org/assignments/media-types/ index.html • IANA MIME type assignments, includes recommended file extensions. • http://en.wikipedia.org/wiki/Content_negotiation • HTTP Content Negotiation.
static resources with Apache • http://vocab.deri.ie/void • Vocabulary of Interlinked Datasets (VoID) • http://vocab.deri.ie/void/autodiscovery • VoID Autodiscovery via a RFC5785 .well-‐ known resource.
classes for describing documents • http://purl.org/NET/mediatypes • Linked data for MIME types (for use with dct:format) • http://tools.ietf.org/html/draft-ietf-http-alternates • “Alternates” HTTP response header (expired draft)
#programme — is used to differentiate information about the programme itself from the document describing it by giving them distinct URIs which are both dereferenced to the same document. • Dereferencing this URI results in a request for the URI without the #programme fragment identifier.
Content Negotiation when requests for this resource are received. • A successful response will contain a specific representation of this document, and include a Content-‐Location header identifying it. • You can copy and paste from the browser address bar into a linked data consumer application.
that they prefer application/ rdf+xml, they will be delivered this resource which contains a description of both itself, and of the programme (identified by its “thing” URI).
HTML RDF/XML Includes an Accept header Content-Location: http://www.bbc.co.uk/programmes/b01cpfvb.html Content-Location: http://www.bbc.co.uk/programmes/b01cpfvb.rdf representations server picks a suitable representation based upon the Accept header
application/rdf+xml' http://www.bbc.co.uk/programmes/b01cpfvb > GET http://www.bbc.co.uk/programmes/b01cpfvb HTTP/1.1 > User-‐Agent: curl/7.21.4 (universal-‐apple-‐darwin11.0) libcurl/7.21.4 OpenSSL/0.9.8r zlib/1.2.5 > Host: www.bbc.co.uk > Proxy-‐Connection: Keep-‐Alive > Accept: application/rdf+xml > * HTTP 1.0, assume close after body < HTTP/1.0 200 OK < Server: Apache < Cache-‐Control: public, max-‐age=300, s-‐maxage=300 < Content-‐Type: application/rdf+xml < Date: Thu, 05 Apr 2012 09:53:01 GMT < Expires: Thu, 05 Apr 2012 09:58:00 GMT < Access-‐Control-‐Allow-‐Origin: * < X-‐Bbc-‐Licence-‐Url: http://backstage.bbc.co.uk/archives/2005/01/terms_of_use.html < Accept-‐Ranges: bytes < X-‐Bbc-‐Licence-‐Text: Access to and use of this feed is for non-‐commercial use only and is covered by the BBC Backstage Terms of Use < ETag: "307bcc6b5782dcc16c3eadee54bdb336" < X-‐Programmes-‐Host: nolaps402.wtf.nolcontent.net:80 < Content-‐Length: 2077 * HTTP/1.0 connection set to keep alive! < Connection: keep-‐alive
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