We should include HTTP Link headers (`Link: <URI>; rel=“describedby"`, `Link: <URI>; rel=“alternate"`, etc.) in Wikidata HTTP responses for a given entity to point out all its possible different representations plus useful metadata.
These headers let data users and their tools make dacisions without having to load and process the entire resources. They are important if we want the data to be seriously used outside the Wikimedia projects.
== Example: DBpedia ==
```
$ curl --head http://dbpedia.org/page/Concept | grep Link:
```
DBpedia includes, in HTTP Link headers:
* `<http://creativecommons.org/licenses/by-sa/3.0/>; rel="license"`
* `<http://dbpedia.org/data/Concept.rdf>; rel="alternate"; type="application/rdf+xml"; title="Structured Descriptor Document (RDF/XML format)"`
* `<http://dbpedia.org/data/Concept.n3>; rel="alternate"; type="text/n3"; title="Structured Descriptor Document (N3/Turtle format)"`
* `<http://dbpedia.org/data/Concept.json>; rel="alternate"; type="application/json"; title="Structured Descriptor Document (RDF/JSON format)"`
* `<http://dbpedia.org/data/Concept.atom>; rel="alternate"; type="application/atom+xml"; title="OData (Atom+Feed format)"`
* `<http://dbpedia.org/sparql?default-graph-uri=http%3A%2F%2Fdbpedia.org&query=DESCRIBE%20%3Chttp%3A%2F%2Fdbpedia.org%2Fresource%2FConcept%3E&format=text%2Fcsv>; rel="alternate"; type="text/csv"; title="Structured Descriptor Document (CSV format)"`
* `<http://dbpedia.org/sparql?default-graph-uri=http%3A%2F%2Fdbpedia.org&query=DESCRIBE%20%3Chttp%3A%2F%2Fdbpedia.org%2Fresource%2FConcept%3E&format=text%2Fcxml>; rel="alternate"; type="text/cxml"; title="Structured Descriptor Document (CXML format)"`
* `<http://dbpedia.org/data/Concept.ntriples>; rel="alternate"; type="text/plain"; title="Structured Descriptor Document (N-Triples format)"`
* `<http://dbpedia.org/sparql?default-graph-uri=http%3A%2F%2Fdbpedia.org&query=DESCRIBE%20%3Chttp%3A%2F%2Fdbpedia.org%2Fresource%2FConcept%3E&format=application%2Fmicrodata%2Bjson>; rel="alternate"; type="application/microdata+json"; title="Structured Descriptor Document (Microdata/JSON format)"`
* `<http://dbpedia.org/sparql?default-graph-uri=http%3A%2F%2Fdbpedia.org&query=DESCRIBE%20%3Chttp%3A%2F%2Fdbpedia.org%2Fresource%2FConcept%3E&format=text%2Fhtml>; rel="alternate"; type="text/html"; title="Structured Descriptor Document (Microdata/HTML format)"`
* `<http://dbpedia.org/sparql?default-graph-uri=http%3A%2F%2Fdbpedia.org&query=DESCRIBE%20%3Chttp%3A%2F%2Fdbpedia.org%2Fresource%2FConcept%3E&format=application%2Fld%2Bjson>; rel="alternate"; type="application/ld+json"; title="Structured Descriptor Document (JSON-LD format)"`
* `<http://dbpedia.org/resource/Concept>; rel="http://xmlns.com/foaf/0.1/primaryTopic"`
* `<http://dbpedia.org/resource/Concept>; rev="describedby"`
* `<http://mementoarchive.lanl.gov/dbpedia/timegate/http://dbpedia.org/page/Concept>; rel="timegate"`
== Example: BNE ==
```
$ curl --head http://datos.bne.es/persona/XX1718747.html | grep Link:
```
The National Library of Spain (Biblioteca Nacional de España) includes, in HTTP Link headers:
* `<http://datos.bne.es/persona/XX1718747.rdf> ; rel="alternate"; type="application/rdf+xml"; title="Structured Descriptor Document (RDF/XML format)"`
* `<http://datos.bne.es/persona/XX1718747.ttl> ; rel="alternate"; type="text/turtle"; title="Structured Descriptor Document (Turtle format)"`
== Useful links ==
* [[https://www.iana.org/assignments/link-relations/link-relations.xhtml|Link Relations - iana.org]]
* [[https://www.w3.org/TR/powder-dr/#assoc-linking|Protocol for Web Description Resources (POWDER): Description Resources - W3C Recommendation 1 September 2009]] (old, but still useful)
* [[https://tools.ietf.org/html/rfc5988#section-5|RFC 5988 - Web Linking - Internet Engineering Task Force (IETF)]]