Discover an LDN Inbox

The sender must know the appropriate inbox URI to which to send its notification. A common case will involve two systems which use the COAR Notify Protocol to interact on a regular basis. It will also be a common case that a system operates only one receiver, using a single inbox for all of its LDN traffic. In such cases, the sender may already be configured to use a particular inbox URI and will not need to 'discover' it.

However, a sender may wish to send a notification to a service where it does not know the appropriate inbox URI. The sender needs to be able to discover the inbox URI. The LDN protocol provides two methods for this - both require an HTTP operation on a known resource URI (for example, this could simply be the 'home' URL of the service). The LDN discovery mechanism is described in detail - with examples - in the LDN documentation, but it is essentially these two options:

  • make an HTTP HEAD or GET request on the target URL, and use the Link header with a rel value of
  • make an HTTP GET request on the target URL to retrieve an RDF representation (RDF 1.1), whose encoded RDF graph contains a relation of type The subject of that relation is target and the object is the Inbox.

A receiver may change its inbox URI at any time - so long as it makes the correct URI discoverable. For this reason, even if the inbox URI was previously known to the sender, it should not be assumed that this URI will remain the same.

Even if the inbox URI was previously known to the sender, '(re)discover' the inbox URI either on every operation or, at least, periodically.

Discover Notify services

The COAR Notify Project, funded by Arcadia, will develop a catalogue of systems and workflows which support the COAR Notify Protocol. This is intended to help foster the discovery and use of the COAR Notify Protocol in a growing web of repositories and services. This development is scheduled to happen during 2024.

COAR Notify workflows should be registered in the COAR Notify Catalogue.