Network construction: We use the degree of overlap in reference lists to construct a network of all articles in our corpus (a technique called bibliographic coupling). If two articles have non-overlapping reference lists, they are not linked; if they have identical references, the strength of their connexion is maximal. The network is dynamic because a moving time window with a length of five years slides through time, one year at a time, starting with window 1950-1954, then moving to 1951-1955 and so on until the end of our period in 2012-2016. This definition of our network means that two documents that have been published more than five years apart are in the same overall network, but never appear jointly in a time window.
Cluster detection: In each time window, an algorithm for community detection based on modularity optimization is applied to the current state of the network. The algorithm used is a variation on the Louvain method. The panel depicting linked circles is a representation at the level of these communities (not of the underlying documents). Once we have community assignments for each window, basic rules based on proximity of clusters from one time window to the next are applied to determine whether a cluster survives, splits, merges or dies without leaving a trace. These rules generate the polygons (i.e. the specialties) that stretch from the beginning to the end of our period in the first panel.
Keywords retrieval: Keywords represent the words that most characteristically distinguish the titles of the articles in the relevant cluster from articles in the other clusters. The panel with polygons gives keywords for each cluster over its full lifetime. The panel with linked circles gives time-specific keywords. These keywords slowly change through time as a specialty changes its focus.
The article for our project on the social sciences and humanities is in progress at the moment, but our procedure is highly similar to what we did in our project on economics. See this article (and its Appendix for technical details).
This project was made possible by a SSHRC Insight Development Grant [430-2016-00758]. François Claveau was project leader, with Yves Gingras as cocandidate. The main research assistants on the project are Philippe Nazair (from the BIN), Olivier Santerre and Philippe Boissonneault (from the Plateforme en humanités numériques, Université de Sherbrooke).