Crawler to predict the availability of a full text at a given URL
Bielefeld Academic Search Engine covers almost 100 million metadata records harvested from open repositories. The problem is that for most of them, we have no idea whether they link to a full text or not. For instance, this item does not seem to be associated with a freely downloadable full text, whereas this one is.
The goal of this software is to perform this classification (not necessarily archiving the full texts when they are available, just classifying the URLs into open / closed).
This crawler visits the URLs present in the OAI records stored by BASE. If one of the URLs of the record points to a PDF file, we happily mark the record as free to read. Otherwise, we expect to land on an HTML page describing the paper, such as a HAL landing page. We look for meta tags with metadata about the paper: sometimes it contains a link to the full text (as required by the Google Scholar inclusion guidelines). If this link actually leads to a PDF, we mark the paper as free to read. In all other cases, we consider the paper as unavailable.
Crawling 100 million URLs takes a lot of time, so we try to reduce the number of
requests we need to do. This is achieved by learning URL patterns to predict
the nature of a page without crawling it. For instance, we can learn
that https://hal.archives-ouvertes.org/hal-[0-9]*/document returns a PDF
file most of the time,
so when we see such an URL we consider it is a PDF file without actually
downloading it. This classifier is implemented in the urltheory module.