Defrosting the Digital Library: Bibliographic Tools for the Next Generation Web
The approximate relative coverage and size of selected digital libraries described in the section Digital Libraries, DOIs, and URIs, and summarised in Table 1.
Of all the libraries described, Google Scholar probably has the widest coverage. However, it is currently not clear exactly how much information Google indexes, what the criteria are for inclusion in the index, and whether it subsumes other digital libraries in the way shown in the figure. Note: the size of sets (circles) in this diagram is NOT proportional to their size, and DBLP, Scopus, and arXiv are shown as a single set for clarity rather than correctness.