Hi @d_r, thanks for your comment. Let me tackle this from different angles.
First of all, I think it is important to clarify that I4OC does not make available any open dataset of citation data. Rather, it is a group that advocates the open availability of citations and that has continuously discussed with publishers depositing the citation data of their articles in Crossref to make them freely available to the world by means of the Crossref API. These free availability of citation data, then, has been reused by several parties, including companies, to offer (either open or commercial) services: in addition to OpenCitations, there are also Scholia, ScienceOpen, and Dimentions, just to mention a few.
From the OpenCitations side – disclosure: I’m one of the Director of this service organisation –, it implements an workflow that continuously ingest new data into the OpenCitations Corpus (OCC), i.e. the RDF repository of open citation data. As mentioned in the website, the ingestion has been suspended in these months since we are migrating the system in a new powerful infrastructure which will allow us to increase the ingestion rate by 30-fold – thus having additional 0.5M citations per month.
Hopefully, we can complete the full migration in June. However, several services made available by OpenCitations are already up and running in the new infrastructure. In particular, it is possible to access the data in the OCC in different ways: downloading the dumps, accessing the bibliographic resources directly via HTTP in different formats, querying the repository by using SPARQL (a query language for RDF data), and searching and browsing information in the OCC by means of textual-string search interfaces.
In addition, we will announce the release of a quite huge dataset of additional citation information in the next weeks on our Twitter account (@opencitations) – release that won’t be possible without the effort that I4OC has done during the past year.
