OAI-PMH in Omeka S: How to share metadata with other institutions

The OAI-PMH protocol (Open Archives Initiative Protocol for Metadata Harvesting) allows institutions to share and harvest metadata efficiently from digital repositories. In Omeka S, the module OAI-PMH facilitates the exposure of stored data in the platform so that it can be harvested by other systems.

In the following guide, we will learn how to set up the OAI-PMH module in Omeka S, optimizing the exposure of our digital collections for other institutions and platforms. 

Step 1: Installation of the OAI-PMH in Omeka S

Before setting up the module, we must make sure it is installed. 

Installation of the module:

• Download the module from Omeka S Modules.
• Upload the module’s file to /modules within our installation of Omeka S
• Go to Administration > Modules in Omeka S and turn on OAI-PMH Repository. 

Step 2: Setting up the OAI-PMH repository 

Once the module is installed, it can be set up in Administration > OAI-PMH Repository module Settings.

1. Setting up the repository’s name

This is the public identifier of our OAI-PMH repository.

• Location: Field "Repository Name"
• Recommended value: Name of our institution or library.
• Example: "National Museum’s Digital Repository"

2. Defining the namespace indetifier 

The namespace identifier is a unique domain which makes sure that the metadata identifiers are globally unique.

• Location: Field "Namespace Identifier"
• Recommended value: Use your own Omeka S domain, for example:
• • oai.mi-institucion.edu  
  • repositorio.museo.org  

3. Choosing the formats of the soon to be exposed metadata 

The module allows exposing metadata to different formats. Select those you will use.

• Recommended options:
• • oai_dc (Dublin Core, required by OAI-PMH).
  • oai_dcterms (Dublin Core extended).
  • mods (Metadata Object Description Schema, recommended for libraries).
  • mets (Metadata Encoding and Transmission Standard, recommended for archives).
• Location: Section "Metadata Formats"

Step 3: Setting up data exposure 

Omeka S allows defining which metadata will be available for harvesters. 

1. Exposing associated media to the items

If you want harvester to direct access to pictures, PDFs or other files:

• Location: “Expose media” Option 
• Recommended value: true (available).

2. Hiding empty sets

For avoiding the exposure of sets which do not contain public elements: 

• Location: “Hide empty OAI sets” Option
• Recommended value: true (display only those sets with at least one public item).

3. Setting up a global repository and site repositories 

Omeka S allows exposing data by two means:

- Global repository: Containing all of Omeka S resources in just one URL (/oai).

- Site repositories: Each Omeka S site has its own OAI-PMH, which is useful for sharing data between entities with the same server.

• Location: Section "Global Repository" and "Site Repositories".
• Recommended:
• • If administering multiple institutions in just one Omeka, the repositories has to be available by site. 
  • If you only have one repository, use the global repository.

Step 4: Customizing set tokens 

1. Customizing set indentifiers 

Each OAI set has its unique identifier. If the format needs changing, new identification schemes can be added. 

• Location: Option "OAI set fomat".

2. Adjusting compatibility with Dublin Core

If metadata refined in Dublin Core Terms is used, it can be merged with Dublin Core standard. 

• Location: Option "Genericize dcterms for specific formats".
• Recommended: true (better compatibility with harvesters).

3. Optimizing OAI-PMH answers performance 

To improve server’s efficiency and to avoid overloading:

- Restricting answers by request:

• Location: "List Limit"
• Recommended value: 50 (Reduce if the server is underperforming).

- OAI session expiration time:

• Location: "Token expiration time"
• Recommended value: 10.

Step 5: OAI-PMH Testing and validating a OAI-PMH repository

Once it is set up, it is recommended to validate if the repository is working correctly.

1. Checking the OAI-PMH URL

Try to access to:

https://nuestro-dominio.org/oai?verb=Identify 

If everything is correct, the repository’s information will be seen.

2. Validating compatibility with harvesters 

You can try harvesting data with tools such as:

• OAI-PMH Validator: https://validator.oaipmh.com/