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oai is an R client to work with OAI-PMH (Open Archives Initiative Protocol for Metadata Harvesting) services, a protocol developed by the Open Archives Initiative ( OAI-PMH uses XML data format transported over HTTP.


See the OAI-PMH V2 specification at

Implementation details

oai is built on xml2 and httr. In addition, we give back data.frame's whenever possible to make data comprehension, manipulation, and visualization easier. We also have functions to fetch a large directory of OAI-PMH services - it isn't exhaustive, but does contain a lot.


Instead of paging with e.g., page and per_page parameters, OAI-PMH uses (optionally) resumptionTokens, with an optional expiration date. These tokens can be used to continue on to the next chunk of data, if the first request did not get to the end. Often, OAI-PMH services limit each request to 50 records, but this may vary by provider, I don't know for sure. The API of this package is such that we while loop for you internally until we get all records. We may in the future expose e.g., a limit parameter so you can say how many records you want, but we haven't done this yet.


Michal Bojanowski contributions were supported by (Polish) National Science Center (NCN) through grant 2012/07/D/HS6/01971.


Scott Chamberlain

Michal Bojanowski