Author: Martin Hepp, martin.hepp@unibw.de

Experiments regarding the support of MIME types (aka media types or IANA media types) and HTTP Content Negotiation for RDF/XML, JSON-LD, Turtle, N3, and NTriples syntaxes.

The purpose of this repository is to test and document whether typical MIME types for Linked Open Data and the Semantic Web are properly derived from local filename extensions and lead to correct MIME type information in the HTTP Response Message header data.

Source code on Github: https://github.com/mfhepp/test_mime_types

Github Pages version: https://mfhepp.github.io/test_mime_types/

Note: The actual payload of the examples is just quickly compiled from trivial examples in the respective specifications or other resources. They might not validate and have no meaningful content.

Files List

File Format Filename Expected MIME Type Github MIME Comment
RDF in RDF/XML test.rdf application/rdf+xml application/rdf+xml OK
OWL in RDF/XML test.owl application/owl+xml application/rdf+xml OK
Turtle test.ttl text/turtle text/turtle OK
NTriples test.nt application/n-triples application/n-triples OK
N3 test.n3 text/n3 text/n3 OK
JSON-LD test.jsonld application/ld+json application/ld+json OK

Status of Github Pages Support

Correct MIME Type

You can always check the current status of support by using curl.

$ curl -I https://mfhepp.github.io/test_mime_types/test.rdf
$ curl -I https://mfhepp.github.io/test_mime_types/test.owl
$ curl -I https://mfhepp.github.io/test_mime_types/test.ttl
$ curl -I https://mfhepp.github.io/test_mime_types/test.nt
$ curl -I https://mfhepp.github.io/test_mime_types/test.n3
$ curl -I https://mfhepp.github.io/test_mime_types/test.jsonld

As of 2024-01-10, all above files return the proper MIME type from their Github pages URIs.

So Github Pages is able to recognize the proper MIME type from the file extension and signal it back to the client in the HTTP response header.

Content Negotiation

Some of the current recommendations for the deployment of Linked Data and Web ontologies on the Web require server-side HTTP Content Negotiation (called “pro-active content negotiation” in the new IETF RFC 7231.

  • https://www.w3.org/TR/swbp-vocab-pub/
  • http://wifo5-03.informatik.uni-mannheim.de/bizer/pub/LinkedDataTutorial/
  • https://www.w3.org/TR/ld-bp/

This can also be checked with curl, see e.g. Richard Cyganiak’s nice tutorial on this.

The very simple case of returning HTML as a default for an HTTP HEAD request without any file extension returns the HTML version, is properly supported:

$ curl -I https://mfhepp.github.io/test_mime_types/test

HTTP/1.1 200 OK
...
Content-Type: text/html; charset=utf-8
Server: GitHub.com
...

Ideally, two other scenarios would be supported:

Server-side Content Negotiation for URI without File Extension Suffix

Cool URIs for Linked Data would ideally be supported, i.e. the best-matching representation would be returned baded on the Accept request header parameter, like so

$ curl -I -H "Accept: application/rdf+xml"

for text/html and all available RDF syntaxes:

  • application/rdf+xml
  • application/owl+xml
  • text/turtle
  • application/n-triples
  • text/n3
  • application/ld+json
$ curl -I -H "Accept: application/rdf+xml" https://mfhepp.github.io/test_mime_types/test
$ curl -I -H "Accept: application/owl+xml" https://mfhepp.github.io/test_mime_types/test
$ curl -I -H "Accept: text/turtle" https://mfhepp.github.io/test_mime_types/test
$ curl -I -H "Accept: application/n-triples" https://mfhepp.github.io/test_mime_types/test
$ curl -I -H "Accept: text/n3" https://mfhepp.github.io/test_mime_types/test
$ curl -I -H "Accept: application/ld+json" https://mfhepp.github.io/test_mime_types/test

Status 2024-01-10: Unfortunately, Github Pages always returns the HTML version and ignores the indicated MIME type preferences:


$ curl -I -H "Accept: application/rdf+xml" https://mfhepp.github.io/test_mime_types/test

HTTP/1.1 200 OK
Connection: keep-alive
Content-Length: 690
Content-Type: text/html; charset=utf-8
Server: GitHub.com
Last-Modified: Tue, 03 Nov 2020 16:30:18 GMT
ETag: "5fa1859a-2b2"
Access-Control-Allow-Origin: *
Expires: Wed, 04 Nov 2020 15:43:50 GMT
Cache-Control: max-age=600
Accept-Ranges: bytes
Date: Wed, 04 Nov 2020 15:48:18 GMT
Via: 1.1 varnish
Vary: Accept-Encoding

303 Redirects

In an ideal world, Github Pages would return 303 redirects for an HTTP request with MIME type preferences that recommend another local file, e.g. requestion application/rdf+xml from the URI of JSON-LD variant, like so

$ curl -I -H "Accept: application/rdf+xml" https://mfhepp.github.io/test_mime_types/test.jsonld

Again, Github Pages simply returns the static file mapped to that URI, in this case test.jsonld with its original MIME type, but neither redirects to a better matching URI nor hints to alternative representations:

$ curl -I -H "Accept: application/rdf+xml" https://mfhepp.github.io/test_mime_types/test.jsonld

HTTP/1.1 200 OK
Connection: keep-alive
Content-Length: 221
Content-Type: application/ld+json
Server: GitHub.com
Last-Modified: Tue, 03 Nov 2020 16:30:18 GMT
ETag: "5fa1859a-dd"
Access-Control-Allow-Origin: *
Expires: Wed, 04 Nov 2020 16:02:11 GMT
Cache-Control: max-age=600
Accept-Ranges: bytes
Date: Wed, 04 Nov 2020 15:52:11 GMT
Via: 1.1 varnish
Age: 0
Vary: Accept-Encoding

References

  1. https://www.w3.org/TR/rdf-syntax-grammar/#section-MIME-Type
  2. https://www.w3.org/TR/owl2-xml-serialization/
  3. https://www.w3.org/TR/turtle/
  4. https://www.w3.org/TR/n-triples/
  5. https://www.w3.org/TeamSubmission/n3/
  6. https://www.w3.org/TR/json-ld11/

Changelog

  • 2020-11-04: Initial version
  • 2024-01-10: Updated status, cosmetic fixes, new theme, wording