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curl -b <temporary cookie file> -O http://<your ACR space>/acr/resteasy/datasets/{id}/file
Adding metadata to an existing dataset would be done as:
curl -v -b \tmp\temp.txt --form "http://sead-data.net/terms/sbdc/ph=6.64;type=text/plain" --form "http://purl.org/dc/terms/isPartOf=http://dx.doi.org/10.1175/BAMS-D-11-00180.1;type=text/uri-list" http:/<your ACR space/acr/resteasy/datasets/<id>/metadata
with the first setting a text value (for pH) and the second setting a URI (i.e. as an external identifier for a dataset that this one is part of).
Collections have an analogous service - simply swap "collections" for "datasets" in the URL used above to set metadata for a collection.
To set a relationship, simply use the identifier of the dataset/collection for the object with type=text/uri-list. For any predicate that has been configured as a relationship, this will automatically create the relation and the reverse relationship.
Curl Tips:
cookie files and the destination for downloaded files need to be in writable directories
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