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PIDA - Persistent Identifiers for Digital Assets

We provide long-lasting references for digital assets accessible to humans and machine agents

Technical Specifications

Secured Communication

PIDA uses HTTPS communication protocol to protect the integrity and confidentiality of data between clients and the service. This is especially important for systems and applications that require high levels of security, for example when managing biomedical datasets.

Content Negotiation

PIDs from PIDA can redirect to any kind of resource on the web (i.e. HTML or else). However, PIDA is capable of content negotiation to be used in semantic web contexts. In PIDA content negotiation for a given PID can be enabled by the user by adding the required information to the submitted .htaccess file.
PIDA supports content negotiation to deliver different representations of a resource from a single uniform resource identifier (URI). When a user or agent requests a URI, content negotiation allows them to specify which representation they require (e.g. document language, file format, or content encoding). Using a PIDA PID, clients can request either HTML or RDF (with different RDF serializations) representations. For enabled content negotiation, requests to PIDs that are coming from non-semantic web applications will be redirected to HTML documents, while those that are coming from designated semantic web applications will be redirected to RDF documents.


Content negotiation can be tested using the curl command-line utility to specify a particular representation of a resource to the same URI. For example:

To request the HTML document describing the scientific events ontology:

curl -L -H "Accept: text/html" https://purls.helmholtz-metadaten.de/seo

To request the RDF file of the ontology, the following command could be used

curl -L -H "Accept: application/rdf+xml"  https://purls.helmholtz-metadaten.de/seo

You will get results that look like:

            HTTP/ 1.1  303  See Other
            Date:  Tue, 22 Feb 2022 14:18:54 GMT
            Server: Apache/2.4.29 (Ubuntu)
            Access-Control-Allow-Origin: *
            Location: https://saidfathalla.github.io/.../index.html
            Content-Type: text/html; charset=iso-8859-1

Windows users can get cURL binaries from here.

Good practice when submitting requests via pull requests

Please help us to issue PURLs from PIDA effectively by following these points when submitting requests:
  • provide your contact info (e.g. name, email, affiliation, etc.) in the readme.md or in the .htaccess file as comments.
  • test your links and .htaccess syntax locally.
  • squash multiple commits into one commit before a pull request. This helps to ensure a cleaner merge history.
  • provide descriptive commit details (e.g. resource name, what changes made, etc.).