How could you make vocabularies de-referenceable? 1.0

4 years ago

Issue

Publishers of data need to be able to handle the various situations in which URIs do not deliver metadata about the resource. 

The discussion on the issue is available here.

Current situation

A recurring issue for Linked Data implementation is that URIs are required as values for properties that link to resources. 

Various collections of URIs have been minted that are being used as the values for such properties. However, resolving these URIs does not always deliver information about the things these URIs represent.

Recommendation

Resolving such URIs should deliver metadata about the resource. Unfortunately, this is not always the case, and if it is the case there are two types of responses to a HTTP GET on the URI. In any case, an organisation that mints URIs should strive to keep the delay between minting URIs and resolving them as short as possible.

Rationale

Resolving such URIs should deliver metadata about the resource. Unfortunately, this is not always the case, and if it is the case there are two types of responses to a HTTP GET on the URI.

  • The case where no response comes back (or a 404 not found) might be because URIs have been minted before the information about the information is loaded on the system. In such cases, a client that has the URI has no way of knowing what the resource is that the URI refers to.
  • In case where a response comes back, there could be two types of responses: either the response contains information about that individual URI, or the response contains a file in which information about the URI is combined with information about other URIs, for example in a schema file.

Clients need to be able to handle these various situations which may not always be straightforward.

Example

The example is based on the Nobel Prize catalogue, which is available via http://www.nobelprize.org/datasets/dcat. Some modifications were made in order to clarify the guideline.

First case (no response): data.europa.eu/3rx/EUProgramme/ contains information about that particular URI.

Second case (response): https://www.w3.org/ns/org#Organization contains information about the URI combined with information about other URIs

 

Related issue

A related issue is that the resolution of URIs should be maintained over time. As soon as URIs are made public, they will be included in metadata that will rely on persistent resolution. 

Recommendation

Organisations that mint URI must define a persistence policy for their URIs. 

Example

The European Commission has established a persistent URI policy and resolution service at http://data.europa.eu/ that aims to persistently resolve all URIs that are minted for resources maintained by the European Commission. The EU URI policy has the following characteristics: governance, URI pattern, URI redirection, service level guarantees.