As a harvesting server, your Dataverse can make some of the local dataset metadata available to remote harvesting clients. These can be other Dataverse instances, or any other clients that support OAI-PMH harvesting protocol. Note that the terms “Harvesting Server” and “OAI Server” are being used interchangeably throughout this guide and in the inline help text.
Only the published, unrestricted datasets in your Dataverse can be made harvestable. Remote clients normally keep their records in sync through scheduled incremental updates, daily or weekly, thus minimizing the load on your server. Note that it is only the metadata that are harvested. Remote harvesters will generally not attempt to download the data files associated with the harvested datasets.
Harvesting server can be enabled or disabled on the “Harvesting Server” page accessible via the Dashboard. Harvesting server is by default disabled on a brand new, “out of the box” Dataverse.
Once the service is enabled, you define collections of local datasets that will be available to remote harvesters as OAI Sets. Once again, the terms “OAI Set” and “Harvesting Set” are used interchangeably. Sets are defined by search queries. Any such query that finds any number of published, local (non-harvested) datasets can be used to create an OAI set. Sets can overlap local dataverses, and can include as few or as many of your local datasets as you wish. A good way to master the Dataverse search query language is to experiment with the Advanced Search page. We also recommend that you consult the Search API section of the Dataverse User Guide.
Once you have entered the search query and clicked Next, the number of search results found will be shown on the next screen. This way, if you are seeing a number that’s different from what you expected, you can go back and try to re-define the query.
Some useful examples of search queries to define OAI sets:
A good way to create a set that would include all your local, published datasets is to do so by the Unique Identifier authority registered to your Dataverse, for example:
Note that double quotes must be used, since the search field value contains the colon symbol!
Note also that the search terms limiting the results to published and local datasets are added to the query automatically, so you don’t need to worry about that.
A query to create a set to include the datasets from a specific local dataverse:
where NNN is the database id of the dataverse object (consult the Dataverse table of the SQL database used by the application to verify the database id).
A query to find all the dataset by a certain author:
where YYY is the name.
Complex queries can be created with multiple logical AND and OR operators. For example,
(authorName:YYY OR authorName:ZZZ) AND dsPublicationDate:NNNN
Some further query examples:
For specific datasets using a persistentID:
(dsPersistentId:10.5000/ZZYYXX/ OR dsPersistentId:10.5000/XXYYZZ)
For all datasets within a specific ID authority:
For all dataverses with subjects of Astronomy and Astrophysics or Earth and Environmental Sciences:
(dvSubject:"Astronomy and Astrophysics" OR dvSubject:"Earth and Environmental Sciences")
For all datasets containing the keyword “censorship”:
Every time a new harvesting set is created, or changes are made to an existing set, the contents of the set are automatically updated - the Dataverse application will find the datasets defined by the query, and attempt to run the metadata export on the ones that haven’t been exported yet. Only the datasets for which the export has completed successfully, and the results cached on the filesystem are included in the OAI sets advertised to the harvesting clients!
This is in contrast to how the sets used to be managed in DVN v.3, where sets had to be exported manually before any such changes had effect.
Important: Note however that changes made to the actual dataset
metadata do not automatically trigger any corresponding OAI sets to
be updated immediately! For example: let’s say you have created an OAI set defined by
the search query
authorName:king, that resulted in 43
dataset records. If a new dataset by the same author is added and published, this does not immediately add the extra
record to the set! It would simply be too expensive, to refresh all
the sets every time any changes to the metadata are made.
The OAI set will however be updated automatically by a scheduled metadata export job that runs every night (at 2AM, by default). This export timer is created and activated automatically every time the application is deployed or restarted. Once again, this is new in Dataverse 4, and unlike DVN v3, where export jobs had to be scheduled and activated by the admin user. See the “Export” section of the Admin guide, for more information on the automated metadata exports.
It is still possible however to make changes like this be immediately reflected in the OAI server, by going to the Harvesting Server page and clicking the “Run Export” icon next to the desired OAI set.