OAI, short for Open Archives Initiative, was born with the aim of facilitating access and retrieval of academic material published electronically, ePrints. But at present, its purpose is also to facilitate the widest possible consultation of digital resources, and of funds and/or collections related to culture, science and digital education.
This is a widely used standard that is based on a very simple exchange message protocol and the encoding of records according to the Dublin Core metadata scheme, ISO 15836. This allows you to describe this type of documentary information in a simple and very flexible way.
The address of the OAI repository on this website is https://catalonica.bnc.cat/catalonicahub/es/oai/oai.do